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.
With P2P marketplaces, you can choose offers you like (mk4 told you already) and you can choose the marketplace that gives you cheapest fees for your trades (as I know, fees tend to be different for buyers and sellers. Usually fees are more expensive for sellers, and fees for buyers almost have free of fees with trades). For bank transfers, there are additional fees and determine by the bank you use to transfer your money.
Have free rights to choose offers and marketplaces, banks, etc. You will be almost get freedom on P2P marketplaces but be aware of scammers on such. Don't be attracted by any words, any promises, anyone to trade off Escrow. Don't release your bitcoin if you don't get your money from your trade partners.