Not too long ago, I had a chance to speak to one of my credit card account holders, a Discover card account I only used to transfer a big chunk off another credit card so as to lower overall interest and continue feeding my credit habit, as it turns out. See, my primary credit card, the one first given to me by my primary bank, is really the only one I use. Not only have they, over the years, upped my available credit up to $20,000 without my requesting it, they have always been extremely liberal with minimum payment requests. This is why, over the past 12 years or so, I have gladly availed myself of this card, and every time the balance got too bloated, I'd simply transfer a healthy chunk of it over to a new, promo interest card - pay that one off, or transfer the balance back to my primary card if I'd not managed to pay it all off, and presto. Wash, rinse, repeat.
But as I try to get some current balance information from the Discover people, they keep interrupting me, as I speak to them, about all the cool perks I can have if I actually use their card for more than just that 8-month old balance transfer. They might as well go out and ask me, outright, "why don't you use it more? Don't you like us?" Let's see, there are cash rewards (only a 2%), airline miles (I can't afford to go anywhere), a free hat (what? are you kidding?) and some new even more special promotion for those who've no used the card in a while (I can't even remember it right now).
So then I simply ask "so, were I to use this card for all these exceptional cash-back options, what would the interest on those purchase balances be?"
"14.5%"
"I see. And is it not true that were I to make any purchase with this card, whatever balance I put on it, no matter how small, would be paid last - every payment going toward the 4% promo balance?"
"yes"
"Basically, even if I bought $100 worth of stuff so as to earn 5 bucks and a hat or whatever, I'd be paying 14.5% on that $100 until I paid this whole thing off?"
"yes"
"and why would I want to do that?"

Compare that to my habitual card. They've never offered many frills, just a pretty standard cash back reward program. They've never offered an amazing promo APR deal, though their regular APR has never gone above 9%. They don't harrass me with idiotic promos and stuff every blessed time I call, and overall are very decent. They give you decent rates, give you enough rope to hang yourself, and are very pleasant to deal with.

Then there's the matter of the minimum payment. That Discover card always had a draconian mimimum payment schedule - always enough of a percentage that it forced me to pay anywhere from $150 to $200 a month. Not only did this make me feel less kindly towards them, but it made me careful to not let the card situation get out of control, so that even if I had been charging on it, my irrational charging behaviour would have been checked by the awareness of this hefty minimum charge. My habitual card, on the other hand, not only charges only 0.5% plus finance charges, but they also, as they explained it to me the other day when I called them, apply any payment you made the month before to the current one due. This has meant that, over the years, I have noticed months go by without a minimum payment coming due. Literally a whole year, sometimes, of owing $0 per month. So here's a scenario where you give a clueless 20 year old a credit card with a huge limit, let them be, and then not even ask for a minimum payment consistently - what does said clueless 20 year old do next? Buy a plane ticket to Rome.

THe result? A ten-year old permadebt balance of $15,600, on which I've probably actually spent $8000. An accumulation of misinformation, leniency in payments, and overall ease of dealing with the people has paid off considerably for these folks

That, my friends, is how you create customer loyalty.