My impression is that many of the sellers who add a fee for Paypal also accept checks or money orders, which cost them nothing to deposit and collect through the banking system. So, they look to recover the Paypal fee, which would otherwise reduce their net proceeds.
For myself, when I sell, I only accept Paypal, for a variety of reasons satisfactory to me (and I don't care what anybody else thinks on the subject, thanks very much - I have yet to have an item fail to sell, either here or on eBay, where I also buy and sell). For that reason, I always indicate that I will absorb the fees. But I have on several occasions paid the Paypal fees when buying - I just factor the fees in when evaluating the "buy it now" price or when figuring out what I will offer. I figure it is the seller's right to decide what forms of payment to accept, and whether to require the buyer to pay the Paypal fee. A buyer who does not like the payment terms and total price should pass on the purchase.
For myself, when I sell, I only accept Paypal, for a variety of reasons satisfactory to me (and I don't care what anybody else thinks on the subject, thanks very much - I have yet to have an item fail to sell, either here or on eBay, where I also buy and sell). For that reason, I always indicate that I will absorb the fees. But I have on several occasions paid the Paypal fees when buying - I just factor the fees in when evaluating the "buy it now" price or when figuring out what I will offer. I figure it is the seller's right to decide what forms of payment to accept, and whether to require the buyer to pay the Paypal fee. A buyer who does not like the payment terms and total price should pass on the purchase.