Sometimes when I'm buying online, it does bother me to find that "other" people have a coupon for something I want and that if I REALLY want it, I will need to pay full price. It specially bothers me when I'm a returning costumer and didn't receive any e-mails letting me know of a sale or coupon. This situation applies to other situation as well, for instance, think about the couple (or single person) that signed a contract to rent a place, has been a great tenant, and would like to renew the contract that is now ending soon. However, instead of the landlord saying: "hey! you have been a great tenant, so I will NOT raise your rent (or as much), so I can keep your business for longer", he/she says (thinks): "I know you like it here, so I'm going to stick it to you and raise the price of the rent, while new people who I don't even know, will get a cheaper rate and possibly not be as good a tenant as you are".

Sites should definitely keep track of loyal costumers and offer coupons in this manner and allow one to enter then once logged in, but not trouble visiting costumers with this. Letting people know they could have gotten something for cheaper is usually a discouragement from click the "place order" button. I know have definitely just x-ed out of my tab at that point in several occasions.