First Published Model (Classic Wooden Chair)

Welcome. You did a good job with the model. I think the design is one that has been featured in a popular Blender tutorial, so there has been a lot of this chair style for sale and for free lately, but that's ok since yours is free to download too. Once you start creating models for sale, you will need to also create more preview renders of the object from various angles, and more wireframe renders as well. Preview renders are best if you create them in 1920x1080 HD. This will clients to get a better view of the model. If you create textures, try to create PBR compatible texture maps. PBR is the industry standard these days, and will also help sales. Above all, be sure your models are original, and keep modifiers like subdivision surface intact in the native file format, so clients can choose to reduce or increase iterations as they wish.

Once again, welcome to CGT, and I wish you much luck and success in the future.

I believe you did an awesome job for a first timer. There are some points which can definitely help you do better, though.

- It's better to use no environment, when you're creating a model for sale. At least not for the signature image (the image which is going to show off, or illustrate you work)

2- Adding a wire-frame image is really a good idea, and from as many angles as possible. However, it seems like you have used the wire-frame modifier and cycles, which is not really suitable. I highly suggest that you use free-style line of Evee. It's quite simple to use and has astonishingly better results. here's a link which shows you how to do it smoothly:
https://www.youtube.com/watch?v=BhJnC4TRJT4

The rest of the things is just like luxxeon mentioned.
Can't wait to see more models from you.
Best wishes.