A few years ago I got on a kick making simple Photoshop templates and threw up a website to try and sell a few. I had no illusions that my templates were of the level that were being sold for $20+ so I went with a type of credit system similar to what iStockPhoto.com does. A visitor buys a set of credits and uses those credits to buy templates. Seemed like a simple process and after a little tinkering with WordPress I had a working setup.
But after two years only 3 people had bought credits and I had made a whopping 12 bucks.