I am unsure if I can sell my box spring, if so then how?

Donate it to a charity in your area. I work for a charity in Arizona. We have a program called Special Needs. A person can contact us if , for example, their house burns and they loose their belongings. We'll give them whatever they need from a bed to a dining table to a small TV to baby carriages, pots and pans and so on. Totally free. They just have to show us the Fire Dept Report or the Police report to prevent fraud.