There are good people everywhere and there are bad people everywhere, and everything in between.
The thing which I have found, during my 9 years of aircraft ownership, is that it is almost impossible to find a UK company about which there is a consensus on them being good. It is extremely easy to find a company on which there is a strong consensus of them being dodgy. For the USA, OTOH, it is not hard to find a company with a good reputation. You have to ask on
US pilot forums, etc.
I would never suggest the USA doesn't have d*ckheads in the business; there are loads and I think their avionics business is just as hit and miss as the UK scene is on the whole. The USA has just the same % of avionics shops capable of
delivering a new HSI installation with the glideslope reversed; the main difference being that it is a lot cheaper to get work done out there
However the undeniable thing is that a US engine shop (e.g.) will be 10x bigger than a UK engine shop and this means they are going to be doing any given type of engine a lot more often, and it also means that if they screw up there will be many more owners writing about it. So due diligence is much easier to do.