my first 3D model on CG trader

Search for rim lighting, it's a photography concept that will make your renders better, specially for hard surface. Also, add wireframe renders to your preview images.

I agree with lucasbenicio. The preview renders need to be improved to show off the model in a better light and you'll need to use better materials. Also, wireframes are a must if you are trying to sell for games or VFX because topology is very important for rigging characters for animation. Especially for games, buyers will need to see your model's wireframes to know if it will fit into their pipeline. You mention also that the character is better than many others because of the hands and chest, so you should have some closeup renders of those areas if you are pleased with them to show them off better to the buyers.

Presentation is everything when selling game or VFX models. It's an important aspect of selling anything, but especially for games or VFX. Buyers need to see the details and the craftsmanship.