telling someone to post a good review could be considered a bribe
But really, isn't the point of the review to find out not just where you're doing good, but most important where you're doing bad? This would help you improve in that area.
Personally I put a lot more weight into reviews that we receive that are critical of staff, systems or resources - it gives us the opportunity to improve. If everyone says everything is wonderful, you can quickly find yourself scratching your head while people start leaving because of whatever reason that they didn't alert you to.
Posting a review for the public I guess is one thing, but posting a review for internal improvement is what I look for mostly.