I'm pretty sure you have to disclose sponsored content. So if he's accepting money/free days out he would/should have a note in the description.
He need to put it more than in the description, he needs to tick the box in the YouTube upload section and make a clear statement to the effect at the beginning of the video, and "receiving payment" does not just cover actual cash, anything that can be considered payment in kind or by product (I.e. Free entry, free travel, free food, etc.) is in the ASA's eye considered payment.
If he is not doing this and it's later found that he did receive something in return for a review (even just free entry) he will have his channel closed down by YT because they seem that petty atm, and likely be fined by the ASA, this is not petty jealousy talking either, it's the law and applies to everybody, not just a few.
Of course if he isn't receiving anything then there is no problem.