Earlier quoted context omitted.
If online ad campaigns did not bring sales, a lot of people would stop doing them. There are other advertisement media; there is organic-looking product placement, there is overt product placement and "influencers", etc. Still, people buy a lot of AdWords and similar, and occasionally I see a relevant ad I click. BTW ads within Facebook are usually of much better quality (for me as a reader), likely because they can…
You occasionally click on "relevant" ads? I'm really curious why you would do that? Personally, I'll go out of my way to make sure that I don't buy anything referred to me by an ad, on the grounds that advertising is a vile and parasitic industry.
I sometimes click on ads about things related to IT and programming, if they mention something novel and important, just to be aware of the landscape, and what potential competition are pushing.
I see ads relatively rarely though, because I run uBlock Origin. So the ads I see are usually placed in context with some care, not just randomly tucked on to an unrelated webpage. Most of the ads are really poor, as I can see if I use an unprotected browser.