Seller asked for PayPal fees after the sale. Should I pay them or not?

Ebm, the whole point is that the seller neglected to mention the fees.
The OP (buyer) isn't being a cheapskate, just nonplussed that the seller is asking for the fees after he received payment.

I guess the OP as 2 choices:
Either ask for his money back and cancel the deal.
Or,
Pay the fees and be done with it.

Though, if it were me, before doing anything, I would contact Audiogon and ask them what they feel is appropriate in this situation.
I also hope the seller is following this thread. I would like to hear his/her version of the story.- Just to be fair.
Miscommunication happens. It would be nice if both parties could come to an agreement.

Who is this seller?  Let us know who to watch out for.

In my offers, I always explicitly state it includes ALL fees (shipping, PayPal ...) to avoid confusion.