Credits for repeat purchases. For instance, some percent of all purchases go towards future purchases or shipping upgrades. West marine does this- I get 10 dollar certificates after spending a couple hundred bucks. But please do it online
Also- west coast shipping is a real pain. While I like free shipping, waiting all week for stuff is a pain. And I am not into spending 70 for accelerated. So if there were a way to reward repeat customers with faster shipping....