See I would go completely the other way. A couple of years back my neighbour noted that I spent every weekend outside cleaning my car, interior, keeping it immaculate. She had an 15 year old + BMW convertible 3 series. Probably worth about a grand I thought, it was covered in all sorts of welded on crap, hood had moss etc. Turns out she bought the car new and was the only owner, she loved the car but car washes never worked on it. So I offered to detail it for her, the look on her face when she came out after I get it back to pretty much brand new was amazing she couldnt stop saying thank you, even rang her brother up who then drove over from an hour away to come and look. Clearly the car meant a lot but she didnt have the knowhow to go to a detailer. I couldnt imagine getting the same satisfaction cleaning a supercar and have the owner waltz back in throw me a £20 tip without so much as a second look and just drive off...