Avis sells these Club membership cards and offers the best incentive to its sales agent to sell them. I guess it is every business' top management priority to gain customer loyalty for competitive advantage, and they translated it in their compensation policy (which is the best way to get you message accross to your front line troops, believe me!).
However if you are not ready to pay for price advantage (among other benefits), Avis offered you the Avis Preferred card which gives you great service, that is the possibility to get your card under 3 minutes (they prepare the contract before you arrive). And this card is totaly free! And that is the best thing: offer your customers a free card...next time that they will think about renting a car, they won't check two different rental companies for the best offer, because the best offer was when they chose your membership card!