A pest control company offered $5 to anyone who would post a review that the business itself had written. The moving company was willing to pay $50 but wanted original copy. An appliance repair shop provided a start: “I really appreciate that the service tech was on time, the problem was solved, everything was cleaned up and he was very professional. Please add 50 or more words,” the shop suggested. It would pay $30.

The highest payment was offered by a jewelry store in San Diego, which said it was forced to solicit reviews after others got away with doing it. “We have noticed that some of our larger, corporate run competitors have been unfairly trying to get reviews written for them on Yelp, which puts us at a disadvantage,” wrote Bert Levi of Levi Family Jewelers. He said he would pay $200 for a review of a new custom-designed ring.

Asked Wednesday for his side of the episode, Mr. Levi said, “I need to talk to my lawyer.”

Jessica Hernandez, a proprietor of a Chicago hair salon, was more vocal. Yelp said it had caught her salon, Mirror Mirror, offering $10 to complete this tribute: “You want to write about how you visited Chicago and wanted to get your hair colored and cut for a date you flew out to meet with. You ended up loving it. You happened to walk by and walked in and was serviced instantly. Feel free to add great details of your own.”

Ms. Hernandez said she knew nothing about any efforts to buy a review, but had some harsh words for Yelp. The site had been so aggressive in seeking advertising from her, “if I could physically put a restraining order on them, I would. As God is my witness, they literally would call every 15 minutes. I put a block on my phone.”

She said she doubted the beware notice would have an effect. “People are kind of wary about what they read these days, and hopefully they’re smart enough to know better,” she said.

In one case, the business is already gone. La Pomme, a Manhattan nightclub that Yelp said it had caught in a sting in April, closed shortly afterward. A spokeswoman for the club that replaced it said she could not confirm anything that might have happened in the spring.