I honestly do not know of a way to make it completely safe. I\'ve done some online trading with small things, but when dealing with something like a laptop, I\'ve got no clue.
Too be completely honest, I wouldn\'t probably even trade. Your best bet is to put it on Ebay or somewhere and get some money and than save up for a desktop if you need to, it is at least a safer way.
Edit: I was also thinking about the fact that if you do actually get the item in return, there is the chance that something is defective . or something will go wrong with it and you won\'t have a warranty on it. Personally, trading with something like a whole computer is way to risky in my humble opinion.