It's ages since I've had a negative response or felt like I had to justify why I'm a window cleaner, and it just makes me smile on the rare occasion that people have asked me in a surprised tone of voice 'why are you a window cleaner?', as if I'm bright enough to be doing something else.
I think someone recently asked me if I watched Coronation Street (I don't) but they said there was a window cleaner on there who wasn't the brightest lad in the world. I just shrugged! I don't need to justify why I do this anymore (though I did used to).
Personally, I think the negative perception of window cleaners is helpful. It deters some from joining our ranks because it's not trendy enough for them, and for our customers, they will hold onto us (hopefully), perceiving other window cleaners to be 'burglars in disguise'.