Yes P2P is vulnerable for buyer and seller both. That's why sites that offering P2P they have to do the necessary security checks. Just likes buyers security problem as you explained your friends story I saw a incident where buyer send the INR to seller by UPI and received USDT from the seller and then the buyer applied chargeback in his registered bank.

I used one P2P site where buyer and seller both have to deposit their respective buying and selling currencies/coins in the sites Wallet. The site then work as a mediator and complete the trade. This way fraud activity can be restricted (not fully)