My previous experience is that if you go to a (non dealer or specialist) garage and ask for a service you get an oil change, and maybe an air filter if you're lucky.
The other scheduled items, for example valve adjustments, coolant change, cabin filter, even spark plugs all get skipped unless the owner specifically asks for them.
Your average garage will not know the service schedule of every vehicle, and they never ask ahead when you book what is required or ask info about mileage and previous services so they can look it up. They just book you in, and when you turn up for a 'service' you get an oil change and sent on your way.
My service book has lots of stamps but there aren't any annotations in the box or ticks to suggest that scheduled service has been carried out. I make the assumption it hasn't, which is why I'm working through all the serviceble items. The spark plugs were well worn and the cabin filter I'm pretty sure had never been changed.
You seem to have a very trusting and starry eyed view of dealer services. There are tales on here of people that have put their car (GD I-DSi which was supposed to be every 25K, our Jazzes did 5 x that and tappets never touched) in specifically for a tappet check / adjustment and as a precaution have put dirt on the screws that would need to be undone to do the job, car came back with dirt untouched - but they were charged the £300+ and outside of the car had been cleaned. I myself have bought 2 and 3 year old cars from main dealers and when I came to change the oil the filter was red rusty on the outside, also the air and cabin filters were black coal (and original factory Japanese ones).
If you get a relationship with with a independent garage you will have good service, and they have databases to look up what needs doing on every car.
You pay through the nose for dealer service and normally get the car cleaned and a cup of machine coffee, the rest of your hard earned money ( £80 and hour and climbing) goes towards the overheads of their nice shiny showroom and extra un-productive staff you can see sitting and walking around with a piece of paper in their hand. The easiest thing for a dealer is to bring the stamps in service book up to date in any car they get traded in, and tick a few boxes.
My wife had a Fiat Punto CVT a few years ago and it started playing up, sometimes would not take up the drive when pulling away (or trying to anyway LOL) - the dealer had the car for 3 weeks and replaced ECU (moaned about the £1500 but it did not fix the problem) - when car came back it still had the fault as well as some empty coffee cups and plastic bottles in the rear. I then took car to local garage and described the fault to them, he called his mechanic in and relayed my story, straight away the mechanic said 'that will be the switch on the brake pedal playing up' he ordered one and I took the car back a few days later, charged me £15-00 including fitting - car was perfect after (well as good as a Fiat is ever going to be).