If it was that easy/obvious we would have done that already. Precisely because you can never be 100% sure is why the IP exclusions are there. Otherwise, people would have them banned. If competitors work around the exclusions by proxy switching, then it's nearly impossible to prove and all you can do is add them to your suspected list, ie the IP exclusion list...which takes us back to my original question: If Google Adwords IP exclusion list maxes out at 500 per campaign, then what can one really do? We have 100 IPs we need to add but can't. For more serious webmasters, to stay competitive with Bing's AdCenter, Google's going to have to increase the # of IP exclusions to 2000 or more, or at least, offer a pay-for-more option. It's easy for any webmaster, esp for a large business with a huge number of competitors, to get to 500 IPs. Currently, we're SOL and it makes it hard to compete since the whole system is fraught with fraud and parties benefiting from that fraud or pretending they didn't know. Along with my other Google Stats, like CPC, CPM, etc, I call this stat "IIB", short for "Ignorance is Bliss", which also stands for stupid money, which is one major form of Google revenue.