Even that though only works once, usually. Once a reader spots that something is sponsored content, they don't trust the source anymore and will treat everything that source posts with an eye of suspicion (which, IMHO is a good thing anyway).

I remember awhile back when someone posted that piece about what it's like to be a Youtuber on here, the author specifically mentioned that doing any kind of sponsored content was like playing Russian roulette with her subscriber count/engagement.

It really is a big problem, and distorts the entire pool of valuable information by blending in sponsored content.

https://en.m.wikipedia.org/wiki/Information_pollution