I'm so sorry you're dealing with this.
I'm curious whether you have a "no refund" policy. Sometimes buyers who just don't like an item "manufacture" a counterfeit claim in order to be able to return it. They think that if they're honest and admit that it's not what they were hoping for, they'll be denied a return. Most sellers, even those who prefer not to take returns, would prefer their buyers be honest with them.
I'd send something along the lines of the following:
Dear buyer,
I'm sorry you aren't pleased with the bag even though it's absolutely authentic. I certainly don't want you to feel obligated to keep a bag that won't work for you so as a goodwill gesture, I'll accept the return as long as the condition is as I sent it.
If it's truly authenticity you're concerned with, you are welcome to visit the purse forum's Coach section, the ebay community discussion boards purse board or even to have it professionally authenticated. I don't know who else does Coach but authenticate4u.com professionally authenticates Coach and their findings are accepted by ebay, paypal and credit card companies.
Again, I'm sorry you aren't happy with the authentic Coach bag. Let me know what you decide to do.
Sincerely,
Seller
Beautiful.. thanks, BB, I am putting that text in my tool kit.
I do have a 14 day return policy / refund, exactly for the reasons you state, with terms clearly spelled out. I am also pretty liberal about it, if someone has an issue & contacts me, I am a purse buyer myself. I do know how it is to get something that's not as expected & don't want anyone to keep a bag they hate, at the same time I do try to keep bag renters away lol.. (bad experiences there)
I've not yet heard back from this buyer, am hoping they have had some rest & have been reassured by the evidence that they did indeed get a great deal on an authentic Coach briefcase.
If not.. well.. they gave their phone number, maybe I'll give them a call.