I've only had one 'wrong customer job'.
We turned up at the house and as the arrrangement was to 'just do it' and put a self addressed envelope through the door so as a cheque could be sent , we did all the windows which were really filthy and the frames to.
After we finished the owner came out and asked us why we'd cleaned his windows.
We had the wrong street. He said it happens all the time with the post. His road was William Road and the road we wanted was Willams Road. Willam Road runs into William Road with no clear indication that it does so.
The owner decided to let us finish before saying anything as he'd guess we had the wrong address.