Its not really taking advantage when you advertise the business though
As a user, I'm reading a positive review of a place and I'm unaware this review was posted in exchange for a free meal (in other words, bought).
What bothers me the most is how many people see no problem with that, which feels to me like a much bigger problem we have as a society (essentially: the growing disconnect between motive and perceived motive in information distribution and the fact that everyone is OK w that).
I seem to recall that Kim Kardasian get busted for such.