I am also not too sure how that site works, I am not sure what the procedure is in terms of trading with people there. I only know how to buy from the Marketplace.
With trades, it all depends on the people - if you haven't got anything they are interested in, some will tell you so, other's just ignore the offer completely. There are some though who have work commitments that keep them of the internet for a bit. I know MrHurtado17 will not ship internationally.