There have been some psychology experiments that cast doubt on the naive econ treatment. In behavioral economics, the alternative hypothesis is called the "endowment effect". The short version is that people get attached to something they intend to keep (as opposed to trade onwards) and demand a significantly higher price to sell it than they did to acquire it.

http://en.wikipedia.org/wiki/Endowment_effect

http://endowment-effect.behaviouralfinance.net/