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When it comes to satisfying their customers, most U.S. retailers — both brick-and-mortar and online — are losing ground for the second year in a row, according to an annual consumer satisfaction survey.

The retail sector, which includes supermarkets, discount stores and department stores, slipped almost 1 percentage point to score a 77 out of 100 in the annual American Customer Satisfaction Index survey released Tuesday.

Shoppers are not happy with the “lackluster” and “underwhelming” customer service they so often experience, said ACSI Managing Director David VanAmburg. “Things like courtesy and helpfulness of store staff, call center support and even availability of merchandise on the shelves … have seen drops from a year ago,” he said.

The 2018 ACSI Retail Report is based on interviews with more than 62,000 customers chosen at random and contacted by email between January and December last year.

Online retailers

While Americans clearly prefer shopping online, even e-commerce showed signs of strain, dropping to an ACSI score of 80, down 2.4 percent from last year.

Customers surveyed did not see any improvement in the online shopping experience since last year and felt most aspects of the process — including desktop checkout, navigation and site performance — have deteriorated. Mobile apps are the one bright spot, earning high marks for quality and reliability.

The big news: Online giant Amazon, which held the top spot in the ACSI survey since 2010, plunged 4 percent to score an 82. Costco, which made its debut in the online category this year, scored an 83, to beat Amazon and lead the pack of the 25 internet retailers surveyed.

“Costco is the value leader among online retailers and its Kirkland brand may be part of the reason why, offering quality products at a lower price,” the report noted.

Other internet retailers that did well: Etsy, Kohl’s, Nike and Nordstrom all scored an 81; Apple, eBay, HP Store, Macy’s, Newegg, Overstock, Target and Wayfair all had an 80. Walmart (74) and Sears (73) were at the bottom of the list.

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Department and discount stores

Costco also takes the top spot in the department and discount store category, with an 83. Sam’s Club is close behind at 80. Both had the same scores from last year, even though customer satisfaction with the category dropped 1.3 percent to an ACSI score of 76. The third warehouse chain, BJ’s Wholesale Club, scored a 79 to take third place in a tie with Dillard’s, Kohl’s and Nordstrom (which saw a decline of 2 percent).

“Costco and Sam’s Club have figured out that customer service is critical, and they invest in it more than the bells and whistles we typically associate with other big-box retailers,” VanAmburg told NBC News.

Several chains took a big hit this year: Fred Meyer, which is in the process of a major overhaul, dropped 5 percent, while Meijer was off 4 percent.

Walmart’s score rose 1 percent, but with a 72, it’s in next-to-last place. “Walmart’s checkout speed is the slowest in the industry and its staff are less courteous than its competitors,” the report said. Beleaguered Sears, which struggles to say alive, slipped another 4 percent to score an all-time low of 70.

Supermarkets

The nation’s supermarkets also took it on the chin, with customer satisfaction in this category down 1.3 percent, for an ACSI score of 78. Except for convenience of location and store hours, all elements of the grocery shopping experience were worse than last year.

Shoppers said brand names are less available and merchandise selection is lacking. They also felt the quality of the meat and produce has fallen, the stores aren’t as clean as they used to be, sales are less frequent, and the pharmacy service was worse.

Supermarket apps were included in this year’s survey for the first time and scored an 82 for quality and reliability, but website satisfaction dropped 2 percent to 80. Stores that don’t get the online component right will have difficulty competing as online grocery shopping becomes more popular.

Two traditionally high-performing chains, Trader Joe’s and Wegmans, continued to shine with even higher scores this year. With an ACSI score of 86, Trader Joe’s is not only the highest-rated supermarket, it’s the highest-rated retailer in this survey. Wegmans is a close second at 85, followed by Aldi and Publix at 84, Costco (83), H-E-B (82) and Sam’s Club (80). Walmart holds on to its perennial last place, with a 72, down 1 percent.

Why do Trader Joe’s and Wegmans take the top spots year after year? “They take great care of their employees, which results in happy employees who are trained that the customer comes first, and they are to do what they need to do to make sure the customer experience is a great one,” said industry analyst Phil Lempert, who runs the website SupermarketGuru.com.

The big news in this category: Whole Foods dropped 2 percent to score a 79, which puts it in a tie with BJ’s Wholesale Club, Hy-Vee, Kroger and ShopRite.

Considering the importance of retail to overall consumer spending, the continued decline in customer satisfaction cannot be taken lightly.

The ACSI report suggests high employment is putting a strain on customer service because it creates staff shortages and constant turnover.

Customer experience expert Jon Picoult, founder of Watermark Consulting, also blames short-sighted management who are dealing with competition from Amazon and other online-only retailers, by neglecting the in-store experience.

“While that might help bolster financial results for a few quarters, it has a very insidious long-term, consequence of undermining one of the few remaining sources of competitive differentiation available to traditional retailers in their battle with online rivals,” Picoult said.

Fewer employees, poorly trained staff and long lines at checkout “all sour people to brick-and-mortar stores and drives them into the arms of online retailers who offer greater convenience,” he said.