It is hard to say who gains more in a transaction.<p>What can be said is that in most transactions both parties walk away with more value.  It is guaranteed to be a positive sum game -- value is guaranteed to be created.<p>The violation of this rule tends to happen if one or both parties will lose some value if they do not make the transaction, in which case they will try to minimize loss rather than maximize gain as measured by the value they entered the transaction with.  This is the essence of exploitation.<p>These more varied classes of transactions can be a positive sum game -- where one party gets more value than the other loses, a zero sum game where they cancel out or a negative sum game where one gains less value than the other loses or they both lose but less than they would without the transaction having taken place.  It is not guaranteed to be a positive sum game and value could be destroyed overall.<p>This simulation, where wealth is maintained at a steady state not only overall but within every transaction, is not really possible.