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Your preview renders are too low resolution/pixilated. Most of your shots are out of focus (turn off DOF). Make all the backgrounds consistent. Prices are too low - low price usually reflects low quality. No standard exchange formats such as blender,max,c4d etc.
I assume you are aiming for some pixel art style, which is fine I suppose if that's something people are looking for but if that's the case add more detail in the textures - check other models on artstation in that category. Your customers are skilled 3D artists so if you save them time its worth buying, no offense to you but most artists could make these in about 5 minutes.
