Mark.
You raise a lot of interesting issues here. No one can really know the answers because this is uncharted territory. I think:
(1) if someone buying chips, let's say, wants to call the payment a "gift" in order to save the seller PayPal fees, I think he should ask the seller in advance if that is OK with the seller. If some seller gets loads of "gift" payments, which PayPal thinks is a method of fee avoidance, PayPal can implement this policy of theirs: bar the seller's PayPal account from accepting any payments as personal payments like gifts.
(2) it looks very suspicious if the seller is always sending off PayPal-generated shipping-postage labels to the person who just sent him a "gift" payment.

But if the worst thing that can happen is that the PayPal account can no longer accept gifts, one might ask "What is the big deal?" "Take the chance."