I've been thinking about this a lot recently, but haven't come up with a strategy that would ensure a fair trade scenario (Assume, for argument's sake that I am well-stocked in most items, but find that I lack something of vital importance; a medication, a source of protein, a certain caliber ammunition, etc. and am the 'weaker' party in this situation). I also have a valuable item or service to trade. Any situations I can think of would inevitably come to one of two conclusions: a) the party with greater firepower simply eliminates the weaker party and takes what they want or b) doesn't trust the weaker party to deal in a symmetrical fashion (i.e. they set a trap) and therefore the deal never happens, and neither party benefits. In many ways, this is similar to a hostage exchange. How do I ensure that I get what I need if I am the weaker party?