There are many companies and products to help us stop fraudulent orders from entering systems. Some are good, some aren't, all are expensive. As a result many, many ecommerce shops create their own prevention mechanisms.
One that I've seen fairly effective (especially with international sites) is device fingerprinting. The theory is that your IDS system tags every user entering the system with a unique key that identifies a particular device. Once a user is flagged as fraudulent, that unique key can be used in the future to automatically flag new orders - even if the user registered new acccounts to place the order.
If your running a multi-site system, this could also be utilized across all of them to give you a higher level of detection (power in numbers). We recently implemented a jQuery plugin version of this device fingerprinting that has given surprising results. This is by no means a catch all, serious level of protection but it's definately going to stop your amature con-artist.