03/20/2015 (Fri) 16:07:22
In the broad sense of the word, what anon said can sometimes not be true, as some people are asinine greed buckets who are not content to agree with the trade.
However, seeing as things have different value for different people depending on their percieved elasticity value and replaceability by other products, you can surmise that close to all trades are adequate once you realize that all trades are voluntary.
This could be further explored by remarking that a "wallet or life" situation is an inadequate trade, which I reply to you that it's not so much of a trade as a forced/coherced action where the other party is given an understanding that if things don't go in a way which is undesirable to him/her, said person will end up losing something more precious (possibly their life).
So, adequate payment is something that can't exist in a sophist sense, but in a different and more practical facet of what is a complex world view, you get to function in a society with an approximate definition of "adequate payment" which is foundational to commerce. Keyword here is "approximate".
Then there's things like convincing the other person that he's receiving adequate payment, which wether or not being true, still makes for a valid trade when things are done freely.