i was going to do a deal with a guy on Craigslist. he told me that a ps3 i was buying. was 500gb. when i got home i found out that it was only 80 GB?

There is not much the legal system can do cost-effectively to help you. You may be able to persuade him to rescind the transaction. Other than that, for the relatively small dollar value of the items in question, it's not likely that you can solve this problem unless you are willing to go to small claims court.