Why sales are low?

One sale in two months isn't that consider the numbers of models you. Get more published and you will eventually get more sales.

Hi there,

You have fairly good modeling skills but very boring renders. All items are preferred presented in gray and depressive tones, it's not a good choice for regular successful sales.
Make more contrast and colorful juicy renders with HDRi maps that will create good highlights and reflections for metal and other materials on your models.
Also, add close-up renders of the most interesting places in the models.

Learn the basics of perspective, projection, as well as compositing and post-processing renders.
Without this knowledge and with such renders, there will be no good progress in sales and attention to your models, even if you upload a large number of models.

With the right approach (without rush and laziness), everything will definitely work out and provide you with a stable income. Good luck!

Best regards.