Who would wanna be cashless, in a cash business?
Those who want a cashless car wash do so because they look at being cashless as more convenient, theft and safer.
Do I believe that? In my case, no. I've spent way more time dealing with credit/debit card matters than I have with cash-related matters. I've dealt with far more card outages than I have cash outages of all bill
changers being down, and our cash use predates our
credit card acceptance by two decades. Then there are those "lovely" credit/debit card fees.
With or without cash, there is going to be theft. Anybody who is determined to be a thief will find a way. I know there are customers who will lie about their
credit card having been accepted.
As for safety, I doubt a cashless society will stop that. Smartphones have
credit card info on them. I'm sure some robbers would demand cash transfers. Sure, there are dumb criminals who would get caught that way, but they had to do something dumb and harmful to get caught.