James with respect, its easy for some people who are geared towards that area of tech as such, when advising others as an installer, its not just to try get the work, before anyone stumps up, but its also to protect someone from causing themselves even larger costs for a job that doesn't warrant it, if you can see they're not very savvy with these things, no offense to others btw, as I don't know others levels of knowledge of these things.
Most people on the street etc, would never dream of stripping a wheel of, airbag, column etc, so yes they have the diy option, but you have to be honest that the systems they're working on can become damaged if things are not done correctly & they need the correct tools that most don't want/need after doing some mods, so its cheaper to pay someone to do who has the tools etc that are used often, given I've been to some right hash ups in my small time working in this area of technology.
Overall its not hard to do, but you also cant go into it blind either, as how many times on various forums do you read of people doing things themselves & they say oh dear I broke something because I didnt know etc etc.