Edit: I have called Paypal and discussed with them my situation. Like requested I sent them all of the evidence I have. They apologized and said they will try and fix this. Now I just have to wait and see what happens. I will gladly let everyone know the end results once this is all done with.
Okay, so apparently a client of mine just issued a charge-back. Now, this is the thing; the work has already been done and sent to them, they even posted it in their gallery. Said payment was sent on December 13, 2012. Commission was completed on December 20, 2012.
How do I go about fixing this? I feel if I discussed my case with Paypal, they would automatically take the client's side because I don't have any evidence to use. I honestly don't think I can just say, "Hello. [name of client] had paid me to do an art piece for them. They sent me the money and the work was completed in a timely fashion, and they were pleased with what I have given them." and they'd automatically take my side, so I don't know what to do.
And the thing is, this person apparently has been issuing charge-backs to all of the artists they've ever commissioned. However, at the time I did this commission, I was not aware of this. So what do I do?