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

I recently purchased an item and after accepting my offer the seller asked for PayPal fees (3%). I checked the listing and nothing was listed in the ad about my paying the fees.  I have already payed half the fee but I'm not sure if I should have paid the full amount. Changing the deal after accepting the offer feels wrong to me. Looking for guidance.
+1 @lowrider57 - The deal you made was not to pay the fee but if you feel like you were getting a good deal in the first place, you may want to go ahead and offer to pay half of the fee to get the item you want. The other side of the coin is that if you do agree, then after reading this thread, some sellers may feel more empowered to try this tactic to get more money from buyers over and above what was agreed upon.

I have done a lot of buying and selling on this site, and when I am buying and am making an offer on an item, I always specify that my offer includes any and all fees such as paypal and includes shipping so there is no misunderstanding later on. Good Luck,

If the seller didn’t ask for Paypal fees in the ad, then you’re under no obligation to pay them. If you paid half the fee...good for you, but you had no obligation to pay and the seller has no right to ask. That’s the simple answer!
Does Audiogon have a written policy about a seller adding PayPal costs when  the listing is silent about who covers PayPal fees?