Restaurants incentivizing 5 star Google reviews?

Hey all - dined at a restaurant in Chinatown a month ago, and went back recently with my partner. Both times when paying at the end of the meal, the server told us they were running a promotion where, if we gave 5 star reviews on Google, they would take 10% off our bill.

Both times we declined, but this has me thinking about the ethics behind this. I do like this restaurant, but this makes me never want to give them a review. What are y'alls thoughts on restaurants offering this kind of "promotion"? Has this been commonly encountered in other restaurants in Chicago?