They use their business card ...
... and stamp the back so that you can earn store credits.
Let me explain how it works. You get a stamp for coming into the shop and for every $10 you spend. They have three auctions every week and so for every five write in bids you also can get a stamp. Once the card is full (10 stamps) it is gets the full stamp across it and it has a $1 value in the shop and $2 towards any auction items. You can also trade in a full comp card for five raffle tickets. (They do a drawing for a box about once a month). I did that once and ended up winning a box of Opening Day.
Anyways, I'm curious to know if any of your card shops have anything similar. Let me know.