There was a burrito shop that had a frequent customer card that you could use to earn points towards a free menu item. You could register the card online and for whatever reason you could add multiple cards to the same account.

A friend of mine realized that if you registered a new card they would give you a decent chunk of points just for signing up, then you could merge that account in with your existing account and get free points.

Every chance he got he would grab handfuls of the cards, activate them all, and get tons of free food.

I do this, but recently had the realization that my small percentage of cash back is sourced from the fee the credit card company charges to the vendor. After this realization I now prefer to pay cash when dealing with small local businesses. I’ve even found a few places that will give you a discount for not using a credit card which is quite nice.