Buying reviews is a bad idea, generally speaking. Search Engine Land recently did a piece on the potential drawbacks and risks for businesses that decide to do it anyway. Here is an excerpt:

Brandon J. Huffman, attorney at Odin Law, also points out that businesses doing this are at risk for FTC enforcement:

“The FTC looks at whether you got something of value in exchange for your review. The thing of value is usually cash or a free product of some kind, but the positive review you receive is also something of value. So, this is really no different than a typical paid-for review under the regulations. Businesses would need to disclose that they received a positive review in exchange for their positive review.”

The FTC FAQ page on this can be seen here.