As a buyer, pay with PayPal (NOT friends and family, but the real version where a transaction fee is involved) and only use a credit card you have good history with
The only way to get scammed as a buyer is to skip Paypal buyer protections and skip credit card protections. If the seller wants that skip the purchase.
As a seller keep your fingers crossed, use the PayPal fee based services, control the shipping service(never use the buyers shipping account) and require a signature.
You can still be scammed, though. It is not possible to avoid some risk as the seller.
I have been contacted by scammers here and it was very obvious. Don't fall for obvious scams, if it sounds to good to be true, it most likely is.