Agile, I think that you need a better class of customer....Dead customers are very bad for business and it is a devil of a job to get a guy to sign a cheque when he is wearing hand cuffs...
Skyper.. Aside from the very good and valid points made by all of the other guys, allow me to bore you to death with the story of the one and only time that I was dumb enough to get involved with a DIY heating installation which I had quoted for to fit and commission the boiler and gas supply... the customer had run the pipework to the wrong place, he changed his design of the kitchen without consultation to a place where the flue would have been not suitable...Delay the job whilst he ordered the flue extension from B&Q.. then was the issue of filling the system, after he had assured me that the system was water tight (Quit how he knew, I'll never know).... Every joint and connection leaked... the guy had produced a fantastic sprinkler system... Bearing in mind that like you he was on a budget and at the end of it, had a pregnant wife, no heating and masses of work that needed doing, I ended up fixing all of the joints for free, put other jobs booked in off, inconveniencing other customers.... Despite the fact that they were broke, they had plenty of expensive stuff, like Play Stations, hifi, big flat screen TV.... Shame that they didn't give their heating a second thought.
Would I do another DIY type job?... Not on your nelly, I broke even on the job and I count myself lucky..... These types of job have to be priced assuming that you are a complete numpty otherwise, they just dont work