Genuine Mercedes parts only
That , to a degree , depends on your definition of 'genuine' . Mercedes-Benz have had a policy , for some years now , of sourcing parts from multiple suppliers , yet on most of my cars the build card states that they left the factory with ATE brakes , Bosch or Hella lighting , Continental tyres ; the brands vary from one car to another along the production line .
I have just replaced the front discs and pads on my car , along with the wear sensors , which the previous owner neglected to fit , so the first I knew was when I heard the ominous noise of metal scraping on metal ; the outer pads still had plenty of material left , but one of the inner ones , which cannot be seen without removing the wheel , was right down to nothing . As is my invariable policy , I ordered up a set of ATE power discs and genuine ATE pads and wear sensors from Germany ; I quite simply won't fit anything else to my cars , but if you go to MB and get the blue and white box ; you might get ATE , but equally you could end up with Pagid or Textar components inside ( and I had problems with a set of discs from one of those other brands , won't say which , but they were inferior and they warped within a short space of time , yet still Mercedes OEM , so I consider that a guarantee to nothing ) . You will also find on here , other customers who would prefer Brembo or EBC braking components ; these are all quality parts and another reason why many people either do their own servicing or go to a trusted Indy who will fit the parts they ask for or supply , rather than guessing what they will get at an overpriced dealership .
Similarly , you will find customers who can be specific about which brand of oil you use , or which is their preferred brand of tyres . For many years , I would never put anything other than Duckhams 20/50 into my classic cars ( I loved that lovely green colour ) but then BP acquired Duckhams and now there is only remaining stock . Obviously , later cars call for different specs , and for me , as long as the oil I buy now meets the relevant MB229.xx spec I will be relaxed about using it ; but when I can go to Asda or Tesco and get their own brand fully synthetic oil to MB spec for a fraction of what a dealership will ask for theirs , be it Fuchs or whatever , then that is what I will do ; I still go to the dealer and buy a genuine MB filter , because these cost pennies ; otherwise I'd go for hengst or mann or whatever ; but if I can do my oil change for under £30 all in , that is what I'll do . Also , if you are going to peoples' homes , they won't want any mess ; get a Pela oil extraction tool which will recover used oil without any spillages on their drive ( Machine Mart sell them ) , I've used mine for years and never spilt a drop ; still put a sheet on the ground first , but never needed it .
What you might find worthwhile is doing ATF and filter changes , another routine operation , but not one all DIYers might wish to do ; recharging air con is another easy service as long as the system is working before you start .
So , yes , a bit of flexibility over customers wishes could go a long way .