> trust
This is the key feature. The advertiser risks trusting that the promoter will show their product in a positive light. The promoter risks their own reputation on the quality of their endorsements.
This element of risk hopefully serves as an incentive to maintain a high quality of both the product and the endorsement. Bad manufacturers and poor quality (or scandalous) services should lose access to trustworthy endorsers with (hopefully) large audiences. Good manufacturers and high quality services won't want to associate with cheap shills.
The only problem I see is that places like YouTube are not optimizing for quality endorsers. Their focus on engagement is driving away people that try to create quality; may have already left. Those that remain are becoming increasingly formulaic, uninspired, risk-adverse, and "advertiser safe".
[1] Which is required by law![2] This probably also means disclosing if you got a free copy for review purposes[3] of a product that would otherwise cost money or have a non-monetary value. The disclosure must also be "clear and conspicuous"[4].
[2] https://www.ftc.gov/news-events/press-releases/2017/04/ftc-s...
[3] https://www.ftc.gov/tips-advice/business-center/guidance/ftc...
[4] https://www.ftc.gov/tips-advice/business-center/guidance/ftc...
When I see someone I trust on YouTube recommend a product in a pre-roll ad or the like, then I don't really skip it and I do really keep those companies in mind in case I ever am looking for a product that they might offer.