These are my thoughts on the subject...:
1. The OP checked the oil after the service and found it to be black. He therefore concluded that the oil hasn't been changed. He then went on to further conclude that nothing was actually done, which I assume includes the filters change and various checks etc (other than washing the car). My view is that while the jury is still out on how black should fresh engine oil get in a
Diesel engine immediately after a service, there is no particular reason to assume that any of the other items have also not been carried-out. So we have two possible scenarios here: one scenario is that everything was done as it should and that the oil became black because this is what happens to fresh oil in a
Diesel engine, the other scenario is that nothing at all was done to the car. From reading the posts so far, I don't think there's conclusive proof of either the two scenarios, or anything in-between. In short, there's no proof that the service
was done, and there is no proof that it
wasn't done.
2. Even assuming that the service was indeed not carried-out at all, we should keep in mind that this relates to a particular occasion at a particular dealership. So I think that it would be unfair to tar all MB dealers with the same brush.
3. I agree with the OP regarding the unreasonably-high cost of some of individual services at dealers. Things start to look better when the services are covered by an MB Service Care Plan, but even then, getting good value depends on how the owner plays the system - as we all know, getting a Service A with no additional items done under a Service Care Plan is very poor value - it does not get much worse than that... so owners need to know how to navigate the system in order to get maximum value out of dealer services.
4. I believe that the main reason that dealer servicing is expensive (whether PAYG or under a Plan), is because MB know that owners perceive FMDSH as adding value to their cars come sell-time. So it's in part a financial transaction. However, this is only valid for the more expensive or newer cars. On a basic model or an older car there will be little difference in market value between a car with specialist FSH and main dealer FSH. But, again, it's down to owners to be savvi about it. There's nothing stopping owners from getting their cars serviced - from day one - at a specialist with access to the MB Digital Service Book (DSB). In fact, car manufactures have to facilitate this by law (see Block Exemption) - they are not allowed to corner the market, and they can't refuse a warranty claim simply because the car hasn't been serviced by a franchised dealer. So I would say that, at least to some extent, owners' complaints about the high cost of dealer servicing are unjustified - there are cheaper alternatives.
5. To my mind, the issue of service intervals is a separate matter. There are two parts to it. Firstly, certainly cars are the odd ones out, with the service intervals being specified in miles/time. The majority of other mechanical devices - airplanes, boats, stationary engines etc - have their service intervals specified in hours of operation, not distance covered. Indeed, the conditions under which a city taxi operates are very different to those of an airport shuttle or a regional sales rep's car. So service intervals are bound to be, to some extent, arbitrary. Some large fleet operators do not adhere to them anyway - they will send a sample of the engine oil (and other fluids) to be analysed in a lab and replace it on condition, etc. The second issue is the reason for servicing the car in the first place - I would argue that in many cases, there isn't one... in theory, you could buy a new car, never service it, then sell it after 3 years. Whatever damage or wear caused, will become evident several owners further down the ownership line. So why do we service cars? In part, to retain the resale value, and in part because that's 'the right thing to do' - even if, in fact, we are working for the benefit of unknown future owners.