I disagree. Unless he is paying for the goods/services/products for the customer, in addition to paying them for the reviews, this is extremely misleading and can be viewed as untrustworthy behavior.
Paying for reviews in general is shady behavior for a marketplace, whether the review is genuine or not. I'd advise you not to use the forums to buy these types of reviews.
Quoting for reference, if necessary (archive.is)
Examples would be
Excellent service, repeat customer
Highly recommended
Fast response and delivery
Great customer service and key activated perfectly
Willing to pay in BTC after reviews have been posted. Negotiable on rates