It's very well possible to chargeback as many payments as the sender wishes.
Guess you didn't use paypal as much as I have. If you had read the terms carefully:
"Pay for the full amount of the item with one payment. Items purchased with multiple payments – like a deposit followed by a final payment – are not eligible"
I will send in 2 payments, which is multiple
Therefore it will not be in the sender's favor even if I do chargeback.
It is not possible to win a dispute if you pay an item with 2 different transactions.
Anyway, sending as gift does not allow to open a dispute.
It does not prevent charge back.
You can always charge back if your account was compromised/hacked, and it is the only way people can charge back with virtual goods ... So...