Transact locally. Meet the seller in person, check the item and make sure you are satisfied with it before
you make a payment.
Exchange item and payment at the same time. If you are buying, do not make any payments before receiving an item and if you are selling, do not send an item before receiving payment.
Do not give out your financial information. Starting with bank account details, PayPal info, and any other information that could be misused. Keep them all to yourself.