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

I've had the same experience. No mention of fees to be paid by the buyer in the ad (it would have been contrary to Paypal terms of service) and then they demanded them from me after the Ebay auction.  I declined and suggested that they review Paypal rules and send the item, or I'd be contacting Paypal to complain about his actions and he might lose his ability to use them at all.  Needless to say I didn't have to pay the fees.

OTOH, if a seller states that a buyer pays those fees, that is a contractual term regardless of whether or not it violates Paypal rules, and I would feel obliged to cough up for them as I knew the rules going in.

It is not contrary to Paypal terms of service to ask for the fee. That rule only applies to Ebay. It is an Ebay rule, not a Paypal rule.

The whole PayPal thing sucks.  Man, I miss the day when we sent each other a money order, ship the item when you get the $.  Done deal dude.
Sigh...

There is nothing carved in stone that you must use PayPal. I have sold here and taken certified or personal checks as payment. Of course you don't ship until the check clears.