We have been using the Maxmind minFraud service for a long time now, over 10 years. It is a cheap and effective service in preventing online fraud (costs as little as 1/2 cent per order to screen for fraud).
In the early days we built our own modules to use their API and screen web orders. And for a few years now we have been selling a Magento fraud prevention module that utilises their service. I remember the first day we installed the fraud module in one of our own Magento sites. We checked the most recent 5 previous orders, and one of them (that at first glance looked absolutely legitimate) proved to be fraudulent. So we saved $200 within the first 30 min of setup!
So, Maxmind’s minfraud service has been great for us. And they have been kind enough to do a promo code for us. This code link will work for anyone who wants to use their service, whether it be for fraud prevention, or GEOip databases. It will save you 20% on purchases.
Click here to activate.
Also, they have a service whereby you can report whether one of your orders was indeed fraudulent, which helps them to better improve their algorithms.
If you want some more info on fraud screening and prevention, check out this article: