I use Thriftbooks all the time, but they are really oriented to the USA. It appears they do ship to Belgium but I don't know what they would charge. I doubt they have a good selection of books in any language but English. It shouldn't be difficult to just visit their site, put a book in your cart, and go through the order process until they list shipping charges and taxes. It is not difficult to cancel an order before finalizing it if you don't like the numbers.