Hopefully they won't. You could use this for a serious economy exploit.
Exploit? Uh... every other space video game that involves long travels and merchants base their economy off of exactly what you're calling an exploit. Not just space games either, lots of video games use this as a feature, and a way to make money.
EVE Online - Buy low at one station, sell high at another.
SWG - Buy low, sell high.
Fable (and the lost chapters): Buying sacks of goods, and crates of goods in one town to sell in another.
It's far from an exploit. Real world economics rely on supply and demand and the concept of buying low, and selling high. Why should a video game be any different? The Federation may be a bunch of bunny-huggers who do not place emphasis on personal possessions and profit, but what about the rest of the Universe, eh?