That doesn't seem very realistic. You shouldn't be able to buy something at a low price and sell it at a high price every time, but there could be a chance of that happening.
And maybe there could be a skill ('bartering'?) for this, to increase your skill at haggling.
Edit: And I realize that this feature is a common game feature to keep you from doing this and making a lot of money, but this is supposed to be a more realistic game :)
(Edited by Jadael at 5:57 pm on Dec. 23, 2001)