> strengthen the relationship

This is really the key. The "deal" has to have something for both parties. The vendor gets some kind of lock-in, prepayment, guarantee of future business, whatever it is, and in exchange the purchaser gets a discount.

The discount doesn't just come out of nowhere.

> It's not the deal that made the customer bad, it's that the bad customer insisted on getting a deal

That was indeed the point, guess I conveyed it in a poor way.

This. A bad customer made a desperate situation worse because of their inexperience, neglect, shady motives, or a combination of the three.