The Pareto principle (also known as the 80/20 rule, the law of the vital few, or the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.
This is true in business too. Around 80 percent of your profit usually comes from 20% of the customers. At the other end of the scale, there are customers you really don’t want repeat business from.
One client that runs a large worldwide shop, with a particularly difficult customer demographic needed some decent software to make sure some customers simply didn’t come back. James Spader would be proud of the result.
This blacklist shop module grew into quite a complex beast, fingerprinting the clients OS, looking at network blocks, using all available information, including some very fuzzy matching of postal addresses to come up with a single number that determines whether this client should have their credit card charged.
Of course once charged, we have even more information. We have an expiry date and the last 4 digits of their CC. Unfortunately, this isn’t always unique, even on a country by country basis, so we need to involve a human here.
If this sounds like the thing you might like for your shop, contact me.