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.