Another quick example: I have sold

Another quick example:
I have sold this product http://www.the3dstudio.com/product_details.aspx?id_product=316634 29 times during a time span of 1 and a half years (on all marketplaces). Furthermore, it was initially priced higher that what it is now. I would say that is not bad for less than 2 days work.
You may say that you don't believe that either... luckily I have 11 client reviews only on the3dstudio.com.

Even though you can not realistically hope that all the models will sell that much, it proves that having the right models in the inventory, well made, correctly priced and most importantly, have them ready WHEN the market needs them, you can (at least a proportional scale) make that amount.