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Accepting an answer gives you 2 points. If you then un-accept it again, you'll get -2 points, and if you re-accept it, you'll get the 2 points back. Looking at your profile, that seems to be what has happened.

The same goes for upvotes/downvotes from other people: Somebody upvoted you (+10), clicked again, probably by mistake (-10) and then upvoted you again (+10) on this question. Your other question about TFs has been downvoted once, therefore -10.