Is it possible to sell things back to the shops?
If so, how do I go about doing so?

Yes you can sell commons back to the shop. When going through the shops, view the shop list, and you'll see the SellBack Store towards the bottom.

I will also provide you with the link :) Here. Keep in mind that you only get 50% of what you payed for whenever you sell it back. And you could possibly get up to 75% if you use the exchange thread. :)

Ah, thank you very much.
Super helpful.

This thread can be locked now. :3