I've been working all week in my 4x4 and the customers all though a little surprised have been pleased to see me.
Going from the prices you charge though and that your £10 cheaper on some semis than other window cleaners, I wouldn't worry. The low rates your customers pay means that they should expect you to turn up when you want to not when they want to.
That's why some are charging a little higher, because of days like today when you might not be able to get you work done.
Simon.