I'm not sure that's the best takeaway here, in that it gets the causation wrong. It's not the deal that made the customer bad, it's that the bad customer insisted on getting a deal, whereas a good customer usually knows what quality costs and is prepared to pay.

The takeaway here is probably that the fix isn't just "never discount", but it's to screen for the kind of customer who treats a good deal as an invitation to strengthen the relationship.

> 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.