can you please post on the comment below:
Giving gifts such as free sales promotion to a purchaser is ethical. In this case it benefits both parties. For a customer it may get a coupon off its favorite product or something they need or want or an added product from which can bring happiness. When a customer makes the purchase this benefits the business which brings happiness.
By giving preferential treatment to customers who are also good suppliers. This can be defined as reciprocity, which is the exchange of materials for mutual benefit. In this case I believe it is ethical to give special treatment to customers who are good suppliers. This is creating a reliable customer base. You will c a base that will stick with you because they know they get treated well when dealing with your business. Companies create loyal/reward programs for this reason. You as a customer feel important to this company which is vital for a company to make it as personal as they can.