Well, for us self serve guys it's a bit more difficult. But we installed a system similar to wash carda few years ago called wash remote that lets us do a
loyalty program exactly as you said, tied to the customers
credit card.
They sign up on our website and register their name, phone number, birth date, and the last 4 digits of their
credit card. Once they sign up, they immediately get an email/text message telling them that their next carwash is free for signing up. They can then take the
credit card that they registered the last 4 digits of and swipe it in any of our bays or our IBA's, and they their wash is free. From there, we have many options. Our system will email/text them and remind them on their birthday their wash is free as well when they use the
credit card they registered. We can set up a discount day for members who have registered their card as well. For instance every wednesday if you use your registered
credit card you get 20 percent off. Also, every time they use their card normally, it starts a count of how many times they have used it. On the 10th time they use their card, their carwash is free. The text messages tell them when they are getting close to the 10th one so they know when they are getting their free wash. Basically it's a way to do a punch card for a place that isn't always staffed.
It's probably one of the best systems I've seen that offers something for the self serve operators. I'm sure guys with fully attended washes/tunnels will have plenty of great answers as well.