RE: how do I safeguard myself
Trust is something you either have or don't for another person. Only you can determine if you feel comfortable enough to trust them with your money. This is something you should determine prior to posting an offer in their ad as once accepted, your offer is binding.
You will need to go to Paypal's web site to learn under which set of circumstances they will help protect you. However, one thing you may be able to do is to pay with a credit card through Paypal. Your credit card company may provide protection to you should something go wrong. You will need to contact them to find out what their policies are.
There are two other options. One is to meet the seller and do the transaction in person. The other is to pay COD so that you do not send your money until the item arrives at your door.