I can so relate to that.
We have a painter here at the moment, painting some outside pipes, door lintels etc. He was cornered by an irate owner who tore strips off him because, she said, he had splashed paint on her window. There was one splash of paint on her window, on the inside. It had clearly been there for years. The painter flicked it away with his fingernail. She said well, what about all these other marks? He said, they are bugs, you need to clean your windows………