Ok, here's a tip, I feel like sharing: I recently found my AdSense earnings declining, due to some very low paying flash banners, settling in on my site. The problem with them being, that the advertisers offered stuff for free (so obviously, they couldn't afford to have a high CPC) and concealed their identity by using flash banners, which do not require you to show a target URL. Big problem: How do you find the link target for a low paying flash banner, so you can throw it into the competitive filter, without producing invalid clicks? The answer is so simple, I'm almost ashamed to blog about it, but then again, maybe this helps someone with the same problem.