If you get banned by Google, there is no "guilty until proven innocent". It's simply guilty, end of story.
Well you are one of the extremely few that I saw having the account reinstated, for the rest they are normally banned for life.
I was once an advertiser, I would buy adwords a hefty amount I might say too. Only once did I notice any sort of charge backs and that was because I checked my logs and found a strange click pattern. Then I found the same pattern like a month later and I never got any refund from that. It was only $12.00 but still. Other than that I have never seen anything. And I see people getting banned left and right. I was banned on one account to "protect the advertiser" and I was an advertiser, why would I click ads, i wouldnt want someone doing that to me. I still have an adsense account that makes me good money, but I never ever check the stats, I just get the checks and it has been fine for a few years now. But after they banned me, and they cant tell me why they banned me to protect whatever they do. So now I will never buy adwords again. I use adbrite and a few others now, and I have found I get better results for less money. Oh and my secret account, I only work on it from my friends house, so its a diff IP. They better not trace me...haha...if they do oh well...lots of other fish out there.
Google picks up most fraudulent clicks because the clicks come from the same IP and MACs that the publisher is logging in from. Google has a lot of ways of checking click viability, most peolpe who are claiming they havn't done anything wrong are usually guilty of fraudulent cicks or just making incredibly spammy websites. I personally know one person who honestly couldn't see why he was banend when all his s(h)ites were filled with $1 content from poorly educated overseas workers. As someone who uses adwords on a couple of sites I fully support google keeping spam sites out of the adsense program.