I am all for it but it would be hard to enforce. Ads are already hidden everywhere. Someone "review" a product? Most of the time it is a hidden ad even if the reviewer hasn't been paid with money for that. Watches a movie or a video clip? A lots of products are advertised through close ups on the logos, etc.
Youtubers happily do "reviews" in exchange of receiving stuff, regardless if they can keep it or not. They also know that if they are too critical they may not receive anything more and they don't have any material to review. This was already true on paper magazines.