Half the people on here are the reason I try to avoid Craigslist as much as possible.
If I was selling an unopened computer (anything for that matter), and you came deciding you want to open it up, try out everything, make a new account, and whatnot, I'd tell you to piss off. What happens when you decide to change your mind for who knows what reason? (Maybe you're just screwing with me on purpose with no intention of buying the first place)
That said, congrats to the OP, on the new computer!