When buying a certain number they give a free service

With regard to what some gas stations and stores do, giving their customers gifts such as handkerchiefs or cards to collect for a car-wash or oil-change, or paying a certain amount up front for a discount on each wash, or paying some amount in advance – I do not think that there is any reason not to allow such dealings, because that is like a person giving up some of what belongs to him. I mean the owner of the gas station, laundry or store. It is not like gambling because the person who engages in these three transactions does not lose anything. What he pays is in return for something and any rewards or gifts that he gets are like incentives to do business.