What's the reasonable premium of buying in P2P market vs exchange? That's would be the transaction cost. I would expect BTC or tether price higher in foreign exchange controlled countries like China or Argentina.
Great thing with P2P is that you can choose what price you want, because you yourself can set the buy offer(or of course, choose between other existing sell offers). It's just you might end up waiting a while to receive an offer. As for the price premiums, no idea on that.