Also, Facebook has changed a lot of their rules, so you might need to look into the fine print. I know that at one point both Google & Facebook were not allowing you to "pay" for reviews.. They saw it as bribery, but there are other ways to do the same thing, within their fine print. Ex. a shop does a raffle for anyone that had an appointment/service in that 30 day time frame. So, it encourages setting up appointments in the shop, and then you can post the raffle winner on FB.
Just a thought!