Can be very easily recognized if the DVD can be shipped to your country.
Let's take for instance used copies of Bad Man's River ( yes not the best out there ). Link to amazon.co.uk Marketplacehttp://www.amazon.co.uk/gp/offer-listing/B000096KG0/ref=dp_olp_used?ie=UTF8&qid=1311013300&sr=1-1&condition=used
When it states Domestic delivery rates the seller only ships within the UK when it states International & domestic delivery rates the seller ships worldwide. So for Bad Man's River i wouldn't be able to order it from the seller "wantitcheaper" since i live in Belgium, but i can order it from "zoverstocks" and "Greener_Books"
I would also be able to order it from the seller Zapper since you see the badge FULFILLED BY AMAZON which i guess means Amazon actually does the shipping, but not quite sure about that. Just tried it with that SW and seller and i could checkout.
Same goes for all Amazon sites.
Hope that clears things up a bit.