Do you have vending machines? And are they, perhaps, unguarded? Then you car wash tokens offer you a higher degree of security than real money does. Your tokens can only be used on your own site, thereby greatly decreasing the security risk.
Car wash, tanning centre, car park, launderette, coffee machine... you will already have been paid for it when your client bought the tokens from you.
And they can only use their car wash tokens in your establishment. It’s a guarantee of client loyalty and repeat visits.