You have the message receipts of the deal so if he does dispute it, that should be enough evidence to side with you...
However the "experts" at PayPal may read your message as "Pay me 210 for everything and I'll give you one extra magazine" which this highly intelligent individual also seemed to think you meant. Re-reading the conversation I can kind of see where he got the miscommunication from.
Offer for him to return the replica to you in the same condition it was received and tell him you'll issue a refund excluding fees and postage if he's dissatisfied, 9 times out of 10 that's enough to dissuade them from seeking action AND if he refuses then you have further evidence to prove you did try to handle the situation and he, the buyer, refused your help if he does open a dispute