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.
fgleason
Personally, I think we should accept most buyers will be using PayPal and price our items with the understanding that we'll have to pay a fee. Guess what? Virtually every merchant you deal with who accepts credit cards pays a fee for that service. I never charge PayPay fees but do ask that people consider paying as a "friend" and I've done the same. No PayPal fee but less protection for the buyer. I have a 100% rating here and palm to keep it that way. 
Seller seems like a jerk if it's as you say. You honored your end, seller needs to do likewise. Report extortion to A'gon
I also agree that it was the seller's responsibility to disclose his terms BEFORE the deal. Whacking someone with additional hidden charges after the fact is not an honorable negotiating tactic and holding the item hostage smacks of scumbaggery. You would be within your rights to demand he ship the item as defined in the ad, and if he doesn't like it, then it'll be a valuable lesson learned on his part to be more diligent when posting an ad.