I guess in the end there really isn't anything you can do about it. I've tried using my competitive as filter to block crap advertisers but that seems to not work any more. As for that story that Adsense always shows the most profitable ads on each site, it's a big fat lie. They dump loads of crap ads on small sites so that there big partners can get the good stuff and their advertisers keept happy because they get their cheap traffic.