I had a customer tell me to aerate 3 of her friends lawns, ended up she never talked to them and the 3rd one had an invisible underground dog fence and the line got ruined.
Only once (that I know of) as a tech did I completely treat the wrong property. Although several times I started spraying trees on the right property and treated neighbors trees when there was no clear property line. Once I was accidentally spraying an organic vineyards' sycamore trees and the farmer saw me and freaked out. Fortunately I was only using hort oil and it smoothed over ok.