Actually, Badfish, you're completely wrong.
A change of IP is no causes for a ban to be sure. But the thing you overlook is this:
The VAST majority of people selling accounts do it FAR more than one time.
What they'll look for is not the IP of the person that changes the information, but the IP that was there BEFORE that information was changed.
They'll log that.
Then two or three times later, it'll all go back to the same range and IP (even if it's dynamic they'll have the mac address to ID it.)
Then, it's all over. They'll ban the account of the guy selling, not the people that bought it.
It will take some time, but it will weed out a great deal of it. Right about the time the sellers start getting their accounts locked down, it'll not be worth their while to do it anymore knowing they're "marked for death" if they do it again.
It's far to expensive to buy new computers and ISP's to make it worth while.
I think you dont undertand how this computer and internet thing works.
You can change your IP address every 5 minutes if you want to. Blizz doesnt ban IPs (which would be clearly pointless when you can change it easily) they ban accounts.
New computers? What are you even talking about with this one.