We conduct a second experiment to investigate (1) how reciprocity in response to both immaterial and material gifts develops over time, and (2) whether the observed effects are robust to using a setting where providing extra food requires greater effort by the salesperson.Footnote 9

Experimental procedure—doner

In setting DONER, the experimenters ordered durum doner in restaurants and snack bars. A durum doner, pictured in Fig. 3, is a dish of Turkish origin, made of meat roasted on a vertical spit, and served in a wrap. Providing extra food in the ice cream setting only requires the salesperson to press the ice cream machine’s button just a few fractions of a second longer. In the doner setting, however, the salesperson has to deliberately transfer additional amounts of food to the wrap using tongs. Furthermore, the wrap’s capacity usually binds more tightly (in percentage terms) than the ice cream cones’. We thus consider this second setting to be a challenging robustness check for the findings from the first.

Fig. 3 Sample photos of a durum doner: wrapped in foil (left), wrapped without foil (middle) and unwrapped (right) Full size image

Experimenters bought durum doner from the same salesperson on five consecutive days. An individual experimenter’s role (i.e., treatments NORMAL, COMPLIMENT, TIP) was fixed for each salesperson and we again randomized the experiment (see below for details). We conducted the experiment in Graz (GRZ) and Innsbruck (IBK), Austria, and in Munich (MUC), Germany. In each of the three cities, three experimenters visited the same 18 restaurants, yielding a total of 54 restaurants and 801 individual observations.Footnote 10

Table 3 shows the number of observations per treatment and visit. In some restaurants, salespersons changed during the observation period, such that we obtained more observations for early than for late visits with a particular salesperson.Footnote 11

Table 3 Number of observations for each visit and treatment in experiment DONER Full size table

All selected restaurants are organized in such a way that the salesperson takes the client’s order personally, collects the money, prepares the doner in front of the client and hands over the finished product. Thus, the entire service process is executed by one and the same salesperson. We employed eight male experimenters of similar age (22–26 years), but only three of them collected data in a particular town. One experimenter was active in two towns. Each experimenter ordered one durum doner from a given salesperson on each of five consecutive days. An individual experimenter’s role (i.e., treatments NORMAL, COMPLIMENT or TIP) was fixed for each salesperson. We furthermore strove to ensure that all experimenters always interacted with one and the same salesperson in a given restaurant. We thus designed the experiment to obtain 15 observations per salesperson (three treatments/experimenters, and five observations each). To control for experimenter fixed effects we randomized the experiment. We applied each of the six possible assignments of treatments to experimenters ( N ORMAL- T IP- C OMPLIMENT or NTC, NCT, TNC, TCN, CNT, CTN) three times to cover the 18 restaurants in each town. Thus, each experimenter played each role six times (for five visits each) in each town. Again, the experimenters entered each restaurant independently from each other and were never present in the restaurant at the same time.Footnote 12

After exiting the restaurant, the experimenter weighted the doner as is, i.e., including the tin foil the doner was wrapped in (the weight is negligible in comparison to the product weight and does not vary systematically across treatments). The experimenter noted the weight and put the doner into his backpack for later hand-over to a charitable agency.Footnote 13 The experimenter then recorded the date, time, restaurant, product price, and tip amount (if any), as well as salesperson characteristics as in ICECREAM. The final experimenter to interact with any salesperson also inquired whether the salesperson was the owner or an employee of the restaurant. The experimenters furthermore took pictures of all durum doner during the weighing procedure (data available upon request).

In treatment NORMAL the experimenter used the standardized wording (translated from German): “One durum doner without sauce, to take away please.” The only way in which the salesperson could provide extra benefit in the interaction (apart from, e.g., being particularly friendly, or gifting the consumer with complimentary goods) was to increase the amount of meat or other ingredients, since the durum wraps are standardized. We deliberately refrained from ordering sauce, because it has high relative density and might add noise. One could argue that getting more doner weight may not be considered beneficial by every customer. However, getting something extra is a typical act of kindness in the service industry (e.g., receiving an additional drink, or a free starter in restaurants).

The five standardized wordings in treatment COMPLIMENT, which were used in randomized order, were:

1. “One durum doner without sauce, to take away please. You have the best durum doner in town.”; 2. “[...] It tastes best at your place.”; 3. “[...] By the way, your durum doner tastes great.”; 4. “[...] I never had a better durum doner than at your place.”; 5. “[...] There is no place where the durum doner tastes better.”

Treatment TIP was conducted analogously to the corresponding treatment in ICECREAM. As a percentage of price, tips varied between 8.1 and 10.3%, with a mean of 9.2%.

Results—doner

Table 4 presents descriptive statistics of raw doner weight in grams and doner weight in grams per euro spent, and Fig. 4 depicts treatment means for both measures (see Fig. 6 in the “Appendix” for a robustness check using first visit baseline-normalized weights). Across treatments, raw doner weight varies from 242 to 802 g, with a mean of 422 g. In NORMAL, raw weight remains relatively stable over time. In COMPLIMENT, doner weight is about 3 g higher in visit 1 and increases substantially over time, to a surplus over NORMAL of 23 g in visit 5. In TIP, raw weight is 17 g higher initially as well as in visit 5. Moreover, doner weight per euro is highest in treatment COMPLIMENT and is lower in treatment TIP than in treatment NORMAL.Footnote 14 , Footnote 15

Table 4 Descriptive statistics: mean, median, standard deviation, minimum, and maximum of raw doner weights across treatments and over time in grams (top panel) and in grams per euro spent (bottom panel) Full size table

Fig. 4 Doner weight in grams (left panel) and doner weight in grams per euro spent (right panel) as a function of time (visit number) across treatments NORMAL, COMPLIMENT and TIP Full size image

Table 5 reports results from panel regressions with salesperson fixed effects (see Table 8 in the “Appendix” for a robustness check using first visit baseline-normalized weights). RAWWEIGHT serves as the dependent variable and we use binary treatment dummies for COMPLIMENT and TIP as independent variables (model 3). In model 4 we add time trends (\(\hbox{TIME}\in \{1,2,3,4,5\}\)) for each treatment to analyze whether the effects of immaterial and monetary gifts change over repeated visits. We also add experimenter and location dummy variables as well as variables AGE and FEMALE for salesperson age and gender. Standard errors are clustered at the salesperson level.

Focusing on raw doner weight, we find a significantly positive overall effect of both interventions compared to treatment NORMAL. The difference between treatments COMPLIMENT and TIP in model 3 is highly significant as well (Wald coefficient test, F(1,72) = 7.44, p = 0.0080). With regard to developments over time, we find that the time trend of treatment COMPLIMENT is significantly positive, with an average weight increase of 4.9 g per visit. The other treatments’ time trends are insignificant by themselves. Furthermore, while the difference in time trends between treatments NORMAL (with a positive and insignificant coefficient) and TIP (with a negative and insignificant coefficient) is not significant (Wald coefficient test, F(1,72) = 1.82, p = 0.1815), the trend difference between COMPLIMENT and TIP is highly significant (Wald coefficient test, F(1,72) = 7.46, p = 0.0079).

In contrast, our main result reverses when we investigate doner weight per euro spent. In model 3M in Table 5 we find qualitatively unchanged results for treatment COMPLIMENT, but marked differences for TIP. Here, we report a significantly negative overall effect of treatment TIP compared to NORMAL and COMPLIMENT. In particular, tipping yields 4.5 g less per euro spent compared to the baseline, while complimenting yields 2.6 g more per euro paid. Adding TIME in model 4M we again find a significantly positive time trend for treatment COMPLIMENT while no other coefficients remain significant. We provide further visit-level statistics on treatment effects in Table 9 in the “Appendix”.Footnote 16

Table 5 Panel regressions of doner weight in grams (models 3, 4) and doner weight in grams per euro spent (models 3M, 4M) across treatments and over time Full size table

Moreover, we can also analyze the data from a principal-agent perspective. The exchange of complimentary food for immaterial or monetary gifts may increase the utilities of the consumer and of the salesperson. Yet it is the principal (i.e., the owner of the restaurant) who pays the cost of the increased goods and material employed. At the same time, the principal may profit most from a satisfied customer, because the latter will be more likely to return and to spread the word among friends, thereby increasing the restaurant’s future sales. In the case where the owner herself serves as salesperson, she presumably derives the same direct utility as an employee salesperson from being tipped or complimented. Thus, the effect sizes in COMPLIMENT and TIP could differ for employee salespeople and owner salespeople, even though the direction of this difference is difficult to predict (Akerlof 1982).Footnote 17

Fortunately, doner are frequently prepared not by employee salespersons, but by the restaurant owners themselves (the same is not true for in the ICECREAM setting). This allows us to study differential effects between employee and owner salespersons. As noted before, the final experimenter to interact with any particular salesperson inquired whether the salesperson was the owner of the restaurant. Since some salespersons changed during the experiment, we were able to obtain this information for all but 84 salespersons.

Table 6 Random effects panel regressions of doner weight in grams (models 3O, 4O) and doner weight in grams per euro spent (models 3MO, 4MO) across treatments and over time and including owner interactions Full size table

In Table 6 we use a random effects specification and add interaction terms of OWNER and treatments as well as TIME, analyzing a potential owner effect for each treatment. We find that owners and employee salespersons react very similarly in all treatments. Although most coefficients are slightly negative, there is only one marginally significant result indicating that owners provide slightly less on average in the compliment treatment (see model 3O). However, this effect vanishes when including time effects for each treatment (model 4O). This implies that owners and salespersons are similarly affected by immaterial and monetary gifts.

The findings from both settings allow us to answer all research questions with results using the same numbering scheme as we used for the questions themselves.

Result 1 Immaterial gifts in the form of compliments prior to the product’s preparation induce positive reciprocity by the salesperson.

Result 2 A monetary gift, given prior to the product’s preparation, induces positive reciprocity as well. On the aggregate, the effect is more pronounced than following an immaterial gift before accounting for the cost of the gift. After accounting for the cost of the gift, results reverse, indicating that immaterial gifts are the strongest intervention when controlling for costs.

Result 3 Immaterial gifts by the consumer lead to increasingly reciprocal behavior over time. Thus, compliments to the salesperson yield positive time effects compared to (1) reciprocity induced monetarily by tipping first, and compared to (2) normal orders.