Many years ago I had a job going around with a Corgi guy as it was back then, fitting cookers, if gas I was his labour, if electric he was my labour, with electric we took are reasonable view I did refuse to fit some, but very few, but it seemed 50% of gas cookers he refused due to something not complying with regulations, cupboards too close was the main one, an inch too low would mean rejection and no effort was ever taken to correct things so they did comply, I am sure the offending cupboards in many cases could have been simply removed but we were on piece work, so to reject as did not comply we got same as fitting it, so we were better off rejecting it.
I lasted about 2 weeks and said never again did I want to work on domestic, he also scared the hell out of me with his driving.
With any normal work the trades person can arrange with house holder to do any additional work required, but with the working for a shop they have a fixed job, and there is no way they can arrange to do extra. So they could be a very good tradesman but their hands are tied, they only have two options, fit it or don't fit it.
I usually use local tradespeople from Trusted Traders and have never been disappointed
Lucky, as a tradesman one does not want to pay over the top for advertising and job finding, but there are two groups who really have no option, those starting off as a sole trader who have not built up a reputation with word of mouth on how good they are, and those who are no good so will get the wrong reputation. Most good tradesman will only belong to organisations they are forced to join, with gas the gas safe, and with electric the scheme providers, and in both cases there is a register where you can find them.
OK some times bad reputation is not deserved, I have an oil boiler with a sticker on it, saying for service call this number, the workmanship was so bad they are the last I would call, however I don't really know if it was them or some one after them. But I am not taking a chance.