Now I have had a look through the excellent photos at my leisure, I have come to the conclusion that this is a copying camera/horizontal enlarger.
There are no front movements on the standard mounted with a small lens and the fact that an additional bellows and additional front standard can be mounted in front of the lens standard is conclusive for me.
I have a similar "apparatus" designed for enlarging 4.5x6cm negative plates to a selection of papir sizes. In the middle of a sliding box sytem, there is a small lens mounted centrally. Yours is just a "super size" system with bellows instead of a moveable box system. The plate to be copied/enlarged is placed at the small end and illuminated by sunlight. The small lens produces an image on the rear ground glass, the distance is adjusted for framing and focus and the ground glass is replaced by the film holder (which could also have papir in it).
It could form the basis for a impressive reisekamera if the "middle standard" is well built and can manage heavier lenses.
The sellers description was very misleading, but quite understandable. He did show the correct mounting in one of the photos.
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