On Swappa we use PayPal for payments because they provide extensive buyer and seller protections.

PayPal helps protect buyers if what you receive is not as advertised or if you buy a device that is later blacklisted. Hopefully it's never necessary, but you can use their dispute resolution process to get your money back from bad seller.

As a seller it's a good idea to get your PayPal account verified before creating a listing.

PayPal does charge some fees on the payments they process, but it's worth it for the protections.