Answer: Reinforcement is a process through which a person is motivated to work in a particular direction. But what reinforce one might not do that for other. Similarly in shopping ideas of gift coupons and other attractive offers might reinforce one person to shop and might not do for other. Along with gift coupons, offers like one on one etc can impact shopping behavior as they work as reinforcement.
Physiology can also play role. For some people hypothalamus may release pleasure hormone which might also reinforce them to work.
Other part is expectancy. This theory works on what outcome you expect out of your behavior. There are customers who are loyal towards a particular brands and become members. Having such loyalty customers expect that they will be getting more benefits. These benefits will also work as reinforcement for shopping. On other side expectancy from the side of seller, can also play role in modifying the behavior of the customer.