I do want to purchase an account but I'm not sure how to go about it. I see a signed message saying you own the account is nice, means that it counts as proof that they changed the ownership over to you. But is there anything else or is that the only way to officially get an account? Does changing the email afterwards mean they can't get it back? It's pretty scary to buy an account even if it's only like $5. Nobody wants to pay for something and then have it taken away.
Well, there is no official way that you can get an account. However, you can always request a signed message from the other party so that you know the account isn't hacked nor is he going to claim it was hacked.
Just deal with a trustworthy guy and you should be ok.