Obviously, paying to get a positive review or to bury a negative review is cheating and should be treated as such.
OTOH, paying to get reviewed honestly is completely OK -- it's how many indie films get noticed. While large studios don't (openly) offer cash, they do entice reviewers with food, drinks, meeting cast & crew, swag, etc. Some reviewers seem to feel pressured, others seem to not give a care. AFAICT, they all keep getting re-invited.