When the seller receives money for a normal transaction via Paypal there's a fee taken out of the payment, usually around 2.8% or so. On a multi-thousand dollar item that's some real cash. But when a payment is sent as a "Gift" the fee is waived (or paid by the sender? not sure) so the seller gets 100% of the money.
It's a violation of paypal policy to receive payments as gifts when they aren't gifts, and if paypal finds out you're doing it they will (supposedly) suspend your account, but who knows how often they actually check this kind of stuff.
It's similar to when people state: "Paypal only if buyer pays the fee" or "add 3% for paypal". This is also a violation of paypal terms of service that can result in account suspension. The person receiving the money is responsible for the fees, not the buyer.
But as with everything... the rules and reality can be very different
If plexi is wrong, I don't want to be right.