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

If it was not listed for fees in the ad .then you are in no way obligated to pay this .
 If you don't want to pay ,then donot if he does not agree .he has to give you a full refund .for you fullfilled your end of the bargain.

IMO all fees should be listed in the origional ad so it is clear to all parties involved.

i agree with the consensus that you shouldn't pay a previously-undisclosed cost. more fundamentally, i've always found it tacky for a seller to lay off paypal fees on a buyer, much as i would object to a merchant laying off credit card fees--paypal is largely a convenience to the seller by enabling immediate, verified payment and various other protections.

I have been on this site for a long time and years ago, it was common practice that almost all sellers asked for the paypal fee in their ads. It's not against any paypal rules to ask for the fee, but it is against ebay rules to ask for the fee. Some people have gotten very lazy when they place ads, not including all available information regarding any fees or other costs, they expect to get. Someone here said communication is the key here. So for sellers, take the time to spell out all of the fees and costs you expect and as a buyer, when making an offer, explicitly state that the offer  includes any and all fees and costs plus or minus shipping.  A lot of gas stations in my area have two prices, one for cash and one for credit. Its the same thing here. The seller has the right to ask (or build it into the asking price) and the buyer has the right not to agree to pay it or move on to the next seller. It's all part of the negotiation.

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.