Ian,
I had a similar customer a couple of years back, where he actually deducted £5 for the use of water and electric of the bill i gave him, i thought he was joking at first, but then realized he was serious :
He was a regular customer but i told him not to phone me in future as i just thought that was cheeky and going to far, he had pots of money and i already cut him a good deal !
He's the only one whose ever mentioned it, most dont normally think twice about it,
In fact most houses i go to during the week i fill up the t/m
steve