I went through some tough times because I felt sorry for punters but I don't take any less that £75 ex vat for a job now. What I found was I'd take all that rubbish on for £50 a time then you get the pan that won't seal, that tap cartridge you can't find etc etc and while you are doing that the £3k bathroom job is running behind and the cheque is not in your hand on time and the bills still come out the bank, without waiting for you to finish a job off.
I did a job three years ago on the cheap for a landlord and he called me today because the pressure is rising on the boiler, which has a five year warranty. He said "They will charge if it's not a boiler problem will you nip up and have a look first." I said "Sure how do you want to pay?" Silence said it all. "How much?" " £90 including the VAT and it's Saturday afternoon but since you are a previous customer i'll go for my standard rate" "But you fitted it and gave me the five year warranty?" "Yes, three years ago, I can't see it being an installation issue at all." So i suggested he check the filling loop and if it's not that to wait for Vaillant.
Now I could have went couldn't I and used some of the £90s worth of fuel I put in my van on Friday, left the family for a couple of hours etc etc. Interestingly enough I haven't serviced it for thae last two years so if the expansion vessel is low pressure Vaillant will bill him and I hope they do.