OMAAT had a
good write up on this.
From reading that, it sounds fairly common across the industry. For those in this community, does it have much of an impact? Unless I actually know someone who has visited a property, I prioritise FT reviews and feedback - that's what makes these hotel forums so useful. After that I'll use Tripadvisor (being careful to weed out bogus reviewers with a single post), Google Reviews and bloggers I trust (typically OMAAT, Raffles or the LoyaltyLobby people).
If Marriott want to pay a staff member at TPG, a magazine columnist or an Instagram 'influencer' to visit properties for free, good for them.