Just learned one of my customers is a flaming liberal. She won't like the future invoices as much as the prior. Since she voted for dipschit and higher fuel prices, she can pay for all of hers and some of someone else's from now on.
I used to do the same thing, sometimes based on the type car in the garage or the bumper stickers. I would charge them double; next stop the lady is listening to Rush and her charge is halved. It works out the same.
