Retailers love that price-matching guarantees attract shoppers. At the same time, they hate it when customers actually try to take advantage of these policies.

Walmart has had a price-matching guarantee for years, and Target and Best Buy have recently introduced their own policies on a full-time basis — which even include matching prices with online competitors like Amazon.

In some ways, it seems inevitable that stores would get on board with price matching. The rise of “showrooming” and increased transparency in the marketplace all but forces retailers to either match prices of competing stores and websites or risk losing sales to them. And yet, even as pricing is becoming more transparent, the price-matching policies employed by some retailers remain something of a mystery to shoppers.

Bloomberg News recently rounded up many of the gripes consumers have regarding the price-matching policies of national retailers such as Walmart and Toys “R” Us. Mostly, the complaints center on how confusing and frustrating the policies can be, especially because the decisions inside stores to allow or shoot down price-match requests can seem arbitrary. “Shoppers can get confused,” Robin Sherk, a Kantar Retail analyst, told Bloomberg concerning Walmart locations. “They go to different stores and there are different policies — even in the same store, if you go to different cashiers.”

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Part of the reason shoppers will find varying policies is that it’s “up to the local managers what matching they will do,” one pharmacist who has worked at several Walmarts explained. Another reason could be that the policies themselves are complicated enough to not only confound shoppers, but store employees as well. The fine print of Target’s “low-price promise” is nearly 1,000 words long and includes more than a dozen exclusions like “prices advertised only as a percent off or dollar off.” The Toys “R” Us Price Match Guarantee, which the National Advertising Division recently recommended be changed or discontinued because it was misleading, states that stores will match prices listed at toysrus.com — but not for “online-only prices.” (Not at competitor websites, either, unless the purchase is a certain brand of baby gear.)

In Walmart’s case, customers have complained because sometimes stores would match prices of slightly different advertised products — seeded vs. seedless oranges, for instance — and sometimes they wouldn’t. Sometimes price matches weren’t allowed on identical products either. The policies seemed randomly enforced, apparently determined by the mood of cashiers and the willingness of store managers to play ball, leading to frustration on behalf of mystified customers.

How many customers are we talking about? Probably not a large number. Sucharita Mulpuru, a Forrester Research analyst, has estimated that maybe 5% to 10% of transactions involve price matching during the holiday season. The figure is probably even smaller during the rest of the year.

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For retailers, the true power of a price-matching guarantee lies in the way they make stores seem exceptionally generous, without necessarily requiring price matching on a broad basis. Some consumers see terms such as price matching or a low-price guarantee and think that a retailer automatically lowers its prices to match the competition. The implicit message sent to shoppers is that the store is looking out for them. But this isn’t how the policies work at all; it’s up to the individual shopper to monitor prices and ask a cashier or customer service representative to match prices. If you don’t ask, you don’t get prices matched.

And based on loads of exclusions and fine print in the policies, and the many instances of shoppers requesting price matching only to be confusingly turned down, it appears as if even when you do ask, there’s a chance you won’t get prices matched.