If you use ebay then you could. You could also add a small buy and sell sectionusing an auction script, and take a small cut off that. How much do you hope to make from it? I am happy for each of my sites to make me £100 a month, once I get above that, I tend to move on to the next project.
Can I just say something though and PLEASE don't take offence, but you appear to have gone about things arse backwards
The best and most profitable way to make money is to come up with as many ideas as possible, research them for competition and potential (and sub niches), look at monetisation (possible revenue), then build the most profitable first. Building a site then wondering about the best way to monetise it is nuts IMO LOL