How safe is it to pay for an item on Facebook marketplace using Apple Pay?

Apple Pay would require that the person selling has a merchant account and your credit card company would have some recourse through the dispute process.

Apple Cash is a Person To Person cash transaction. It’s different from Apple Pay. First, it’s like handing a stranger cash. If the transaction goes sideways, there is no dispute process. You lose. End of story.

Just ask yourself, are you comfortable handling this person cash? Is it that great a deal? If you’re meeting them in person and can try the item to confirm its appearance and operation, then maybe. But if you’re just hoping it ships and is as advertised, good luck. P2P transactions are intended for family and friends. Not business transactions.