Being a new operator, I'm liberal w/rewashes, refunds, etc. To me, it creates a feeling of customer satisfaction. Nobody likes to get less than they paid for. I would rather operate under the assumption that folks are honest. May seem naive, but that's my perrogative. A person's own individual mindset goes a long way towards creating the type of success they desire, so I keep my own mind on the positive stuff. Plus, I can tell when someone's scamming.
I can also spot a vehicle that needs tar/pitch removal and scrubbing and not just a $7 wash. Got one yesterday; white olds, covered in tree dirt, sap and tar! I used a nice, strong chem., scrubbed by hand in my ss bay, recommended a paste wax (they said 'no thanks') and sent them on their way. My job is to create clean cars. The profits and benefits from offering top level service take care of themselves from there.