There is only one safe way to trade items in DarkOT which ensures that you are not cheated. Click with the right mouse button on the item you would like to trade and select "Trade with ..." from the context menu. Now left-click on the character you would like to trade with. If your trading partner offers something in exchange, a trade dialogue will open up in which you will see the items offered both by yourself and your partner. If you are satisfied with the offer, click on "Accept". If both trading partners have enough space and capacity to carry the new items, the deal will take place. If you do not accept your partner's offer, click on "Reject". If one or both trading partners reject the offer or do not have enough space or capacity, the deal will simply be cancelled.
Please note that any other form of trade (e.g. "parcel trade") is an unnecessary risk you should not take. Keep in mind that thieving is not a violation of the DarkOT Rules.