FWIW they are lying about the letterhead. either that or you spoke to the lowest level floor assistant who didnt bother asking the manager where its kept.
either way, sounds right for maisons' ethos.
did reedo hear back from maison for his sneakers that ripped after minimal use?
paypal could have an easy way to handle fake claims. just mail it in to them, they have their specialists look at the item in consultation with stores and manufacturers. most "fakes" are fakes of luxury items, its a simple step for paypal to authenticate with the luxury brand itself. itll take 4-6 weeks to resolve a claim but claims should be a hassle for buyer and seller, so that its used only as a last resort and not abused.
if its indeed a fake, paypal will refund you fully and destroy the item. fakes should be removed from circulation. seller is blacklisted and paypal account suspended.
if its legit, paypal retuns to you at your expense deducted from your account, case closed.