One thing to help protect yourself is never do Venmo, PayPal, or Zelle because they don’t allow gun purchases. They’ll ask you to say you’re family and friends. That’s a lie and I don’t deal with anyone who asks me to lie or break rules. You won’t have a recourse.
I like USPS money orders because if you send them, they cash them and don’t send your gun, it’s federal. Plus the PO has their own investigators.