Had a nightmare of a customer this week myself actually.. Had cctv all over the premises watching me, constantly phoning me checking my progress of the boiler installation, complaining that a 22mm clipped gas pipe on a wall was "ugly but will have to do". Anyway she asked me to lower a gas pipe 2 inches so it was more aesthetically pleasing, reluctantly I agreed and lowered it. She then wanted me to knock off £100 off the bill because the tiles have 2 drill holes from the previous pipework clip positions.. (the tiles are out of sight above a unit)
Anyway I replaced the tiles the next day, got paid I full and then told her that I am self-employed so I don't have to put up with idiots talking down to me, gave her the receipt and told her to call someone else to service it.