I haven't put enough thought into it to form a hard and fast opinion.
If someone asks to be paid by gift, I just shrug my shoulders and send a gift. Or decide if I want to add the paypal fee to my payment. If someone suggests it's up to me to decide, I usually send gift if a small amount and regular paypal if large. I'm fairly confident that paypal would stop the service if it became a big problem for them.
I usually mix in a "payment owed" here and there. I haven't read the fine print, but it seems to have the same results.
There was one occasion when I tried to send a gift, but paypal didn't allow it for some reason. I seem to recall thinking it had to do with the receiving address resembling a possible business name.....
I don't sell much, but come to think of it, I think my current practice is to not request a gift, but gladly accept it. I build in the cost of paypal gift to my asking price. My last sell I posted an asking price, the buyer asked if I would accept a lower price, I met him in the middle "if he used paypal gift" ........... not sure what that says about my ethics or lack thereof
Also a bit of an aside since Leon mentioned ebay's near monopoly......I bought a card on ebay last night. When I went to pay, I was directed to Propay. Huh?... what's this? I back tracked looking for a paypal option (since I try to run my collecting through a seperate account tied to paypal), but didn't see one. Thought about emailing the seller to ask to use paypal, but decided to not go thru the hassle. It worked fine I suppose.