how can i Convince the customer to buy my products

You need to have at least 100 models to get enough views and likes to be seen well in the marketplace on CGtrader. I see you only have one model. Also, I suggest you put in good wireframe renders of your models as they help buyers see if it is worth buying at a glance.
Good geometry increases the value of the model but also having very good renders is key to selling better and also getting more views. When the buyers look at your main thumbnail render if it looks great they will click else they will not.

You have more free models than models you are selling... that looks very bad and buyers think there is something wrong with your products if you are just giving them away. I suggest you only have one free item on your list.