I sometimes sell 2 or 3 per day, the highest has been 9, sometimes I don't sell anything for a week on here but start selling on Sketchfab and elsewhere. It's a strange world that you can't plan out because you're at the whim of others.
Marketing is another thing, if you're good at it then you will sell stuff.
Keep your chin up and keep posting your models. Eventually, you will find your niche, and the sales will follow.