We've got a few threads here and in the Round Table about paying for reviews: it's generally considered both unethical and pointless.

Unethical because if you're paying the reviewer, they have an interest in pleasing you so that you pay them to write more reviews, so you're unlikely to get an honest review.

Pointless, because the reviewers who charge tend not to be very influential, and tend not to reach the people you'd like them to reach.