When dealing with online sales...

im just curious because i'm trying to sell one of my computer online, what is the safest method to ensure that you receive your payment if you can not deal locally? one time i tried selling something through paypal and the buyer immediately put in a claim that he did not receive his product since there was no receipt and paypal refunded his money back with nothing i could do. i'm not sure how i would have gone about making a receipt or anything because i didn't ship anything, what he bought was a video game account lol.

so basically my question is how do i make sure i get paid when selling something online?