How to exploit the poor – and why

That said, you wrote "exploiting the poor" isn't really a well-defined concept. Actually, it tuns out to be quite well defined:

exploit (verb): 1) to take unfair advantage of 2) to control or take advantage of by artful, unfair, or insidious means

Do I really need to explain this? If we're engaged in a negotiation and I'm rich and you're poor then I might choose to proceed on the assumption that you need my money more than I need your labor, because if I fail to obtain your labor then maybe my profits will go down by some unmeasurably small increment, but if you fail to obtain my money your children will go hungry. So even though the incremental value of your labor to me might be X I might decide to offer you Y<<X (for you non-geeks, that means Y is much less than X) instead knowing that you have a strong incentive to accept this offer even though I would actually be willing to pay you more if you had any leverage. But you don't, so I'm not. Having come to this realization, I might further decide that it is in my interests to deploy my resources so that you remain poor. Of course, I don't think of this as insuring that you remain poor, I think of it as insuring a ready supply of cheap labor. But it amounts to the same thing.

This is the fundamental problem: labor is unlike other commodities. If we have a surplus of wheat that causes the bottom to fall out of the wheat market and excess wheat to rot in silos, the wheat doesn't care. But labor does care because, to paraphrase Mitt Romney, labor is people, my friend. And labor has children that aren't going to stop needing food just because society has no present need for what their parents have to offer in the way of tradable goods and services.