How to have an item sell at the trader but not buy. As ebayshopper says below setting the buy price to -1 will remove the item from the buy list. When you switch to sell mode it will still show in the list of items the trader accepts.
Like this:
class ItemTrashToiletpaper {
type = "trade_items";
buy[] = {-1,"ItemGoldBar"};
sell[] = {1,"ItemGoldBar"};
};
