Usually, these local sellers can be found on social media to offer their services to friends or other people.
I can't think of anywhere worse to find a peer to peer trading partner than social media. The signal to noise ratio on platforms like Facebook or Telegram is heavily skewed towards "noise". These platforms are absolutely rife with scams. Far better to use a dedicated peer to peer exchange such as Bisq or HodlHodl which has safety features such as a built in escrow or reputation system.
For example, if you use Binance exchange you have to send or lock you BTC into Exchange as exchange is middleman during the p2p trade
Binance is a terrible choice for trading peer to peer. You get absolutely none of the advantages of actually trading P2P. You have zero security since Binance take custody of your coins, you have zero privacy since Binance can monitor all your trades, and you still have to complete KYC.