Your audience needs to trust you. If your audience knows you are shilling for someone, they fundamentally can't trust you.
They can no longer trust that you are saying "This is an awesome product!" because you genuinely believe that. Maybe you actually think it's shite, but, hey, you needed to make rent this month. So, whatevs.
I've even seen people on the internet say "I used to read such and such ...until they began getting free samples and the like to support the blog. Then it went to shit and I quit reading."
It's a problem space I've thought about a lot because I blog. I am trying to get my writing supported primarily via tips and Patreon.
If my audience wants quality content it can trust, my audience needs to pay me. If they aren't paying me, "they are the product, not the customer" to borrow a popular phrase.
But selling out my audience so I can eat is not a thing I am interested in doing. It's flies in the face of the very reasons I blog.
Over the years, a lot of quality free content has either gone to shit or gone away. The expectation that good content should exist, but be free, is simply unsustainable.
Quality content takes time, effort and expertise to produce. It needs to pay, or most of the people who are any good will eventually go do something that does pay.
That's just reality.
And then we are left bitching about how there's nothing any good on the internet anymore and where is all the good stuff I remember from the good old days? (A fairly common refrain currently, actually.)