These days a whole bunch of reward programs are the digital equivalent of those green stamps; frequent flyer points, credit card reward points, shopping "clubs", and so on.
Within the last few days I've done more online shopping than usual. I would fill my cart with the products I wanted, fully prepared to pay the stated price .... until, during checkout, I was presented with a field to enter a coupon code.
Off I'd go, back out onto the web, to hunt for coupon codes, and at least half of my orders went through at a lower price than I was originally prepared to pay.
I still haven't figured out the business logic for that ...
They'd go out and buy a car for sticker price, without even attempting to haggle, thereby instantly erasing about 5 years worth of coupon efforts.
Recommended reading: Predictably lrrational by Dan Ariely. He has interesting things to say about behaviour like that!