@Ratimov made a huge list regarding a
[BIG LIST] Buy/Sell Crypto (OTC, P2P, DEXs, CEXs, NO-KYC, ATMs, etc.), you can visit that thread and understand it very well.
Here either you can buy cheaper or you may have to pay more it depend on who is selling ? how many coin is selling ? Who is buying ? How the transaction is made ?
First, what's OTC? It's
"Over the Counter".
So IMO, the platform that has hosted OTC or is an act of an escrow or a middleman between two parties trading transactions could be swapping crypto or crypto to fiat. As I heard, buying and selling large amounts on the P2P transaction or OTC is you may encounter difficulties in trading assuming that on this kind of platform there are fewer traders.
I trust no one except on Bisq and Hodlhodl, they're fully decentralized, and it is very safe to trade p2p.