We had a problem with the boiler in our new house, I called three plumbers, one said he would charge a full diagnostics check but would take the fee off the bill if we went through him, the other two didn't say anything like that.
First guy came and did a diagnostic check, was here for an hour, moving furniture and cupboard backs to see what the problem was (quoted £12k) second one was here for 10 minutes said it it could be a number of things, that they would start with the most likely and work through it all until the problem was solved (quote started at £1.5 to £8k) third one came, spent ages looking around, found a pump that was broken (quoted £250!)
We went with the third (and the problem was solved) when the bill came it was £75 more than quoted, I called the boss, he said that was for the diagnostics call out, I said I had to get back to him, called a solicitor friend, who then called him back, said that we were never informed of the call out fee and so he could not charge us for one. The boss called me back and said that he definitely told me about the call out fee when I called, I asked his name and then told him I didn't speak to him, that I spoke to his father, who is the actual boss but doesn't work as often anymore (all told to me by the plumber who came out to do call out and came back to replace the part) he then told me his dad was old and forgetful and that I should still pay for it, I said that my solicitor says that as you didn't advise me of the call out charge, they couldn't charge me it. He took it off (and his lovely dad came round (for free) to look at sorting out our antiquated plumbing system, was with me for 1.5 hours, told me exactly what needs doing, had a cup of tea and cake and told me about his grandchildren! He also said that no work man can charge a call out fee if they don't advise you of it before they come!)