I get this most with pressure washing.
The old person tells me that their son has a pressure washer and said he would do it, but she says he has'nt got the time as he's got 2 kids and works hard,
she does'nt want to be a burden by keep reminding him to do it, so calls me in.
But when he sees me cleaning it reminds him that he said he would do it......so he isn't happy. Then he works out how much a hour I am charging and he think I'm ripping off his parents. He does'nt realise I have done in 2 hours what it would take him a weekend to do and I will get a miles better result than he could ever achieve.