ok I am getting into this kinda late but anyways ...
I have a lot of experience with ebay and paypal disputes. If the buyer files a dispute and says the item is fake the buyer has to get written proof of this from an expert in the field. Paypal disputes are usually a long and dragged out process. Takes months sometimes for paypal to end the dispute. If you have a dispute against you my advise is do everything you can to draw it out. Chances are the buyer will leave a negative no matter what so who cares about that.
The object is to give them as much trouble and to keep them from getting the money back. Make them go get a letter of authenticity from a expert in the field. Usually this process takes at least a month or more for paypal to come to.
There are plenty of chances for the buyer to slip up and forget that they need to get the proof with in 14 days etc. I am not saying you cheat the buyer ... after all if you are in the right then you are only trying to keep money you rightly earned.
A lot of buyers have tried this crap with me. Keep all the e-mails as proof. If the in the first e-mail the buyer says its the wrong size but later changes the story to its a fake item then you can just send that e-mail to paypal and case closed.
Also ask the buyer to take photos to prove that the item is broken, damaged or that the serial # is not on the tags ... when the buyer takes a photo of the tag and the serial number is there then that pretty much makes them look stupid and you can pretty much automatically win the dispute.
Some guy recently purchased some posters from me .. he says these posters are all wrinkled. Buyer didn't purchase insurance. I tell him they weren't wrinkled when I sent them send me photos of the damage. Buyer later responds "the wrinkles are only on the back of the poster" and buyer decided to keep them. All he wanted was for me to give him a portion of his money back!
A big scam on ebay!
Don't fall for this trick. They will say the item is damaged etc but of course they are willing to keep it ... if you give them back 1/2 the money.
BULL$H!T!!! Tell em to file a paypal dispute. Chances are they will not win unless they can prove that the item is not what you sent ...
O I am on a rampage now LOL ... I just got a cool idea though. Maybe I should write a paypal dispute tip sheet for the forum. Yes Yes I will work on it.