I know nothing about the web advertising industry or how it works with bidding and so on and I don't think I am alone.
So if a site has ads then as far as I am concerned the buck stops with the them: I have no knowledge of the ad setup or what deal the site has and I don't care either - the site owner takes the responsibility and if I have a negative effect (hacked/malware/slow load or whatever) then I won't be back.
If you bought a car and it had a dodgy handbrake then you would blame the manufacturer of the car, not the company in Outer Mongolia that supplies it to them, or worse, the company that supplies them with their plastic... same applies here.