First of all, if you have a history of good posts, then we're going to be suspicious of any plagiarism accusations. Second, if it does happen, you can come to Meta on a new account and explain it.

That exact scenario happened with chimk, and he was unbanned after we found out. And although it was certainly a big mistake on our part to have banned him in the first place, the person who framed him did in in a pretty sophisticated way, and his case was exacerbated by the language barrier (eg. we were unable to immediately determine whether he was a good poster or not).