To add to what @lockiabel said, you should also focus on models that are too difficult for the average 3D artist to do in a timely manner. Its about bringing value to the artist who buys your models. So If it would take me 30hours to model a rattan/wicker chair with intricate details and I charge my rate at $50 per hour that chair would take $1,500 of my time, so if I could buy it instead for $50 that is a very good deal.