Agree to meet during daylight hours in a public place and bring a friend to accompany you. Turn down any request to meet at your house, in an unfamiliar place, or by yourself no matter how big and tough you are.
Do not hand over the item until you have cash in hand. Don’t accept partial payment or anything other than cash for the transaction. If the method of payment changes from your previous agreement, walk away from the deal.
If the potential buyer wants time to consider and comes back later, follow the same procedures. Don’t get careless the second time around.
If the item being sold has significant value, meet inside a bank where you can deposit the money before leaving – this way the buyer can’t turn around and rob you. It is hard to be safer than in a bank where there is plenty of security monitoring.