They NEVER will tell you what invaolid clicks there were, when, etc. So basically, they get free space on yoru site, and get out of paying, and never have to prove why.
They don't give you details on the invalid clicks because it would make things a lot easier for people to reverse engineer the process they use to detect them.
You might have lost $100, but I think it's pretty clear that the amount of money Google could cheat people out of isn't anywhere near as high as the amount of money they stand to lose should Adsense's legitimacy be seriously questioned. Remember, advertising is one of Google's main cash cows. They need Adsense to survive. They don't need to scam a few people out of $100 here and there to survive.
The real question is - how can Google preserve the secrecy of their invalid click determination while still not screwing over people who haven't done anything wrong? Or, alternatively, how can they get the job done without having to keep it a secret?
I can't see any easy answers to those questions, which is why I'm hesitant to start accusing Google of screwing up. Do you have any ideas as to what Google can do in their situation?