See also this thread
https://www.crossfireforum.org/forum...ghlight=Jaguar
Not similar experiences but I can tell you that you are right.
Take a look at any part that is large enough to put the three-pointed star on and you will find a three pointed star. Even the little buttons that are holding the interior panels have a three pointed star.
The engine is entirely MB as are the ancillary components (keep in mind that Mercedes outsources some stuff but it's the same stuff you would find in an SLK.)
Then there are the facts that the car was manufactured for Daimler-Chrysler in Germany by Karmann, in the same factory as the SLK, many Porsche, Audi, VW, and other cars.
The literature on the car comprehensively documents the depth of Mercedes parts that are direct from the Mercedes parts bin.
The body is by Chrysler design, built by Karmann, and those parts are manufactured by Daimler-Chrysler, about 80% of that in Germany.
The whole concept of "badge engineering" is pretty abstract to non-car people. Try telling a Jaguar X-Type owner that they don't really own a Jaguar (it's a Ford Mondeo) and you'll get a whole lot of eye-rolling (and maybe even beat up), but the fact remains it's a Ford that has been badged a Jaguar - no more Jaguar than your sneakers.
You shouldn't worry about those who doubt you, they just don't know and for whatever reason choose not to believe you. If it's really important you could walk them through the car with an SLK parked right next to it and prove it. They might still deny it, just because they're unwilling to be wrong.
You could also do the online research and refer them to the sites that have the info. They'll probably cite a dozen reasons why that too is not right.
But really, you know, so who cares what they think?