There are two facets to this ...
One is "user based":
One is that any member who finds a good (or bad) mechanic should post a review of them, and (hopefully) add them to the dealer directory.
The other is "vendor based":
Dr Andy and Dennis/linden don't really *advertise* ... instead, they have spent hours/days/weeks posting useful information, answering questions, solving problems, telling stories that may not be Sprinter-related. They're exemplary members of the forum, not advertisers of service
(have i ever seen Dennis even post his address?
)
There *are* other mechanic members (sprintguy, i think, and there are others). On the whole, they don't "advertise" for business, but they do post useful information.
There are a couple of dealers, whose occasional posts kind'a stand out as flat-out adverts.
Anyone can also create a *thread* about themselves or any mechanic in the general "sprinter talk" or (if they're T1N specific) under those threads.
They'd be found if someone Searched for their town/state and "service" or "mechanic". (which is probably how i'd look for a mechanic anyway, without recalling that there were "regional" sub-forums)
It's the quality and depth of Andy's and Dennis' (and sprintguy and others over the years) that make them so popular/visible/well-regarded.
It's an open market/forum, so any other mechanic could achieve the same impact.
--dick