I'm still working on that concept.
When I removed my rear sills, that was the case.
Yes, they are like doorpanel clips.
The part that goes into the body is like a plastic anchor that you use in conjunction with screws, to mount something on a wall.
It's kind of barrel shaped, so a trim removal tool with a taper should let you grab the shoulder of it & pull/wiggle it out.

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2007 C 230 Sport.