From Diablo Wiki
There have been numerous trade hacks during the lifespan of Diablo II. Most of these were not actually "hacks" but were just tricks or techniques to rip off other players through trading. This page collects various posts about trade hacks from our Warnings archives. The hacks have been fixed over time, but the social engineering techniques work as well as they ever did, if you're foolish enough to fall for them.
Be smart and don't be blinded by greed; if someone is running something fishy in a trade, or giving you a deal too good to be true, they may be cooking a secret scheme to rip you off.
June 2, 2002
There is a working realm trade hack that's in wide-distribution as of June 1st.
It requires two people to run it; one gives the item to the other, and the hack is able to store the image of their trade for the next person. So you come along and trade with one of them, and see the item he just gave to the other person, therefore trading for nothing. The item can not be moved around the window, and appears in the top left corner. The scammer can not see the item, only you can.
To avoid this, you need to ask them to move the item around in the window, or you could ask them to join a new game to make the trade. As always, be suspicious and careful. A helpful tip from Polarhound.
- Another item to pass along is to always have the buyer make the trading game, and set the max number of players to two. This way not only will the second person required for the hack not be able to get in, but it will stop scammers from having games pre-setup with a "mule" who they have already prepped with the false item-image.