Unlike Google, Yelp seems to be very serious about the quality and trustworthiness of the reviews on their platform. In my experience, Yelp is fairly diligent about enforcing the guidelines they come up with.
One of the agencies I consult with had a client who was using a reputation management company that included Yelp in a widget on his site. The widget asked people to leave reviews. As a result, they received a solicitation penalty from Yelp, which led me to look into its review solicitation policy and how it works.
Yelp confirmed to me it always alerts a business via email before any penalty goes into effect, and the business has 90 days to comply with Yelp’s policies and avoid such penalty.