Ok, replace advertiser with company that wants to display ads. Because that is how you are using it. The ad company is the original advertiser.. this gets even funnier, more please!
Ask the company who uses lots of nails whether hammers work.
I mean maybe the purchaser employee at the company has some conflict of interest around the question -- if they're specialized in evaluating and negotiating hammer purchases they'll not want the company to switch to screws.
But the company as a whole seems to have no vested interest in promoting hammers. They presumably want to sell the stuff they make with hammers and may lie to you about how awesome those products are. But lie about hammers? Why?
Just because someone believes it works doesn't mean it does.
Ad companies sell ads.
Advertisers purchase ads.
Users see ads.
That’s it.