^ Well, yes, true.
But if she had pics of the sunglasses with her tag on in the auction and/or had taken pics of them, with the tag on, in the packaging, just before sealing the package and sending it and had the original receipt, it might, at least, mean that Paypal didn't automatically find in the buyer's favour.
I realise that that still wouldn't be concrete proof that the seller hadn't switched the authentic glasses for fakes, at the very last minute; but it would be a lot of trouble for a fake seller to go to and hopefully, PP would see that.
Also, I believe, if the buyer has claimed the glasses are fake, she has to provide independent proof of that.
Whereas, if she is just claiming that they are not as described, in some other way (but still auth.), the fact that she had used them (which I think could be assumed if the tag had been removed, but can't just be assumed from her having them in her possession for 2 weeks) would mean that they were no longer in the same condition as they were received in (and therefore, PP, again, might hopefully find in the seller's favour [especially as the buyer's already left a positive]).