I was working away and had the headphones in and some woman asked me 'how much'. I pulled one out, gave her a price and said, "But I only do regular cleans!" and she says, "Oh, I only want it done as and when".
"Sorry, I don't do that" I said replacing the headphone ear piece.
Once you've always got a back-log, do you really want this kind of customer? It's fair enough (maybe) if it's some mansion, but for a run-of-the-mill semi, I couldn't be bothered to mess about.