I'm not sure if this is a good place to put this, or if it and other Exploits should get their own thread... either way, here goes nothing.
The store inventory refreshes every time the player reloads a game: this means that someone could look for an item, buy it if it's in stock, save, quit, load that save, and then head right back to buy it again if it's in stock. This allows some of the rarer items to pop up relatively reliably- if you're patient. I'm not 100% sure on this, but I think the slave market inventory might refresh, too. And I know a similar trick can be used for things like causing pregnancy or finding new girls while walking around.
Sure, it requires patience and that the game doesn't glitch horribly from the excessive saving, quitting, loading, etc., but I'm pretty sure it's an exploit worth mentioning.