Reza, I too looked at that website, and the results?
22 reviews of which 17 were complaints/adverse comments dating back to May 2002!!
Of course there will be bad experiences at all garages, I wonder how many complaints could be generated about MB main dealerships since 2002 from the members of this site alone?
I work for an airline and the comments that make the news/review sites are almost exclusively the bad ones. My experience is that few think to compliment, most only to critisize and that is generally in an attempt to claim some sort of compensation. "Good news is not news" seems to be the mantra. Certainly in the airline business some people seem to expect Fortnum & Mason quality for Lidl prices! Forget the fact that they have just been transported 1500 miles in a pressurised aluminium cylinder 6 miles above the earth, safely!!
I am fully aware that National Tyres is not a MB main dealership and consequently I will not be expecting the same level of expertise, but then again I will not be paying the same price. Have you ever thought that the cost per hour is a fixed price irrespective of who does the job? You will pay the same rate for the company's most experienced mechanic nearing retirement with 40 years of mechanical knowhow as you will for the acned grease monkey beginning his apprenticeship (do they still exist?) carrying out the oil and filter change on your beloved MB during a B Service. Granted there may be some level of supervision over the said grease monkey but price does not necessarily guarantee excellence.
I do not have a lift in my garage nor the facilities to change the oil easily myself. I do know how to do it and I am conversant with the mechanicals under the bonnet. In the past, with other cars, I have witnessed the oil change taking place and intend to do the same this time, if I go to National tyres.