I think this is a neat site!
Few thoughts:
1) The black background with gray text is really painful. I think the site would look more "trustworthy" and "professional" if you went with a standard light (white) background, and normal font colour. Easier on the eyes too. The black may deter some people from engaging in commerce on your site, since it's a much more "underground" look. (cool - but again, not so much for a site of this nature)
2) I couldn't actually find any "sort by region" option, or any sort of drop-down to let me pick my country. It's cool that you can click on a flag and then it sorts by that flag, but that means you have to first find an item listed in your country, just so that you can find your flag to click on. A drop-down listing the countries you can choose from would be ideal.
3) The "Next" page buttons, as well as pages for 2, 3, and 4 seem to always be present, even if there isn't a 2nd, 3rd, 4th page. Clicking on "Next" when there isn't a next page takes me to a listing called "Free", with a broken image.
4) This isn't a critique, more of... something that made my morning! From one of the descriptions of old coins:
"Anyone after really ancient coins for shrinking?
These are ideal, some date from the 1900's."
I love it! 12 years ago (1999) is now ancient! Makes me feel... well, ancient