My worst was actually quite satisfying once completed. I did a 2012 Mini Cooper with 65 miles on it recently. The owner expected absolute perfection. Let me say that again, absolute perfection: not one scratch, swirl, defect, chip, unlevelness, or anything other than perfect. We took the job simply to see if we could do it. After day one, she found scratches I didn't even see. We used LED lights, halide lights, flourescent lights, high-intensity spot lights, and good ol' fashioned incendescent lights to find anything we could.
The paint was so soft the when I inspected one scratch my finger nail managed to make an even deeper scratch. When polishing, I would get the scratches out and then have to wait 10 minutes for the paint to cool so that I could touch the car with a new single soft towel. On day one the clients graded me an A minus (extremely high praise from them). A mixture of Fine Machine Polish and Revive Polish followed with Brilliant Glaze and Americana saved the day. After two days the client was happy and now sings high praises of my work, sends us more clients, and even invited us over for a BBQ on the 4th of July. I should metion that the client is one of my favorite clients and I enjoy her company tremendously. If we ever get to do Pebble Beach we decided that this client has to come by to inspect our work before we leave. We learned a lot from this very frustrating detail.