Biggest problem with your collection is that your models are very simple. Buyers won't see value in such models. For any moderately skilled person it would take less time to model something like that, than to search it on the stock markets. Even if you'd increase your collection to hundred models of similar quality / complexity, your sales would still remain low. It is true that for any significant increase in sales you have to have bigger collection (at least 50 models), but at the same time it is very important to increase value of your models. Quality over quantity. For example look at this seller: https://www.cgtrader.com/Kasiopy he has only 21 model in his store, but i can bet that he's not complaining about sales at all ;] Quality sells, quantity helps.