Heard of a number of businesses offering extras or free stuff if a customer would remove/improve/reword a review. This isn't how reviews are suppose to work if they are to be more than an advert/space on platform...
It's also impossible for these review sites to moderate this behaviour on the internet, plus they are only really interested in the internet traffic/ad revenue which pays the wages.
Stick to asking relatives, colleagues or your mates opinion down the pub...