I think SheepGuy was using plateman's magic sign-up bot which comes equipped with its own credit cards, yet isn't advanced enough to change IPs.
Sounds like yet another case of a scripting error on the biller's end that ends up screwing both the webmaster and the program. It very well could be some douchebag attempting to sign-up, getting declined, attempting again, getting declined...lather, rinse, repeat...but the declines are getting tallied as sales. That explains why it's the same IP
and why no one ever logged in to the member's area.