Good points about the store management's decisions to use self checking. Though I hadn't given it prior thought, I am sure you are correct that an analysis has been done. Major retailers like Home Depot are on top of their numbers, I'm sure of that.

As for using a credit card in order to accrue miles or other benefits --- I agree that it's a smart thing to do when managed the way you do (paying off the balance monthly.)

We don't have a credit card that offers miles, but in a similar fashion we use a PayPal debit card to pay for a lot of our business expenses: Being that it's a debit Master Card, it can be used like a credit card, it pulls the money from funds available in our PayPal account (equivalent to paying cash) AND we get something like 3% back on every transaction. That makes a real difference.