I wouldn't say they are getting rich off someone else's crafting. That to me sounds like they are farming the items, having someone else craft it for them, then they go and sell it.
What you are talking about is 'playing the market' ie: buy low sell high. It happens in real life, and it happens in every other MMO...why would it stop in EQ2? If someone finds something they think they can resell higher, go for it. They might just buy the item, then try and put it back up for higher...but nobody buys it...its a risk they take when trying to play the market.