I tried running some PPC ads once, for a month or so. I spent a lot of cash and got nowhere. Curiously I showed a healthy conversion rate on some ads, which encouraged me.<p>I spent an entire day tracking down a lot of these things. Turned out that in every single case, there was no sale, and I couldn't believe in a million years that traffic from these sites were really following my ads.<p>I stopped spending money with Google. A year later they sent me a voucher and begged me to try again. So I tweaked some settings, cut the list right down and spent their $150. Same results.<p>My overriding impression is that display ads, PPC ads and the like are an absolute cesspool of fraud and it's a waste of time trying to untangle the mess.