How can I increase my sales?

You only have 3 models for sale and 33 for free. If it were opposite you would have more sales. So upload mmore models to sell and add more formats.

I would agree with the above, you have a small collection, a lot of your collection is very specific and would have a small buyer pool. Also your giving everything out for free so that doesnt help.
Aside that, quality of your renderings needs to increase, even on the black and white/wireframe types need to be high quality, if i see blotchy spots at low resolution as a buyer i would never purchase the model. So increase the rendering settings and remove the noise in them.

I just opened a store on cgtrader 4 months to sell 4 models and 1 successful project also earns 13 USD, expect many buyers without seeing how to feed life