Re: ...they try to fob you off with jargon
OH yes. We had our boiler fitted by British Gas two years back.
During which they f*cked up the electrics, drilled the vent hole at too sharp an angle so that the drain leaked and made the pipe too short so that it didn't meet their own regulations. They also failed to provide the statutory commissioning document and were unable to locate the engineer's records to supply it a year later when the servicing engineer came ( our own, not BG!).
And yes, the fitters were all - no not subcontractors,- sub sub contractors.
Our services were performed by a Gas Safe engineer recommended by our plumber ( who was recommended to us too).
We had our house insulated recently, under the government's (untimely demised) Green Scheme*. We used a local company, who did use subbies, because that's pretty much how the scheme had to work, and hey we weren't paying the bulk of it. But these were also a local team of small builders. And they weren't going to get the work signed off and paid for unless the work was finished to the required standard. They did such a good job of it that we then brought them back to do some construction work we needed in the garden. It looks amazing.
*Being totally cynical about such things I was signed up to the scheme within hours of applications opening, having done all the preliminary work in advance and found contractors to request quotes which were arranged within days (and even then it wasn't easy -this time the chaos started almost from the first minute).. So that we were already accepted long before its final premature collapse into incompetence. For us it was too good to miss. The house needed this insulation. It also needed pointing. Our contribution was roughly what we'd have had to pay to get the house pointed, so to us there was effectively zero cost for the insulation work.