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I’ve opened an Ultimate Trade on Board Game Geek starting with On the Underground with a goal of finding Hermagor. If you, or anyone you know, are interested, take a moment to have a look at what games are currently in the chain(s). The trade attempt closes no later than 7am September 15th.
BGG supports a very active boardgame trading system but the software only handles locating and transacting direct one-on-one trades. However, an Ultimate Trade starts with a game and usually a target desired game. BGG members post entries on the trade list that name what game they wish to receive (a game already being offered on the list) and in turn they offer another game up for trade. If anyone offers up the target game (or a game the OP is willing to take in lieu of the target game) then the trade is complete, the list closes, and everyone simply sends their game to the next guy in line and the multi-step trade is complete.
Forks are usually allowed meaning that there isn’t necessarily just one end of the chain. For example, if I offer game A and I’m looking for game D, a person might post that they’re willing to take game A and offer B. For game B, yet another person offers game C making the chain A->B->C. A new person also wants game B so rather than being left out of the loop, they create a fork from B offering D making the chain A->B->D. At this point, since D has been offered (my ultimate goal) I can select the winning chaing (A->B->D) and close the list. The person offering game C is left out of the trade loop.