I ended up with one of these today. White, without the upper shell.

I was looking for something to haul a motorcycle with, and this popped up. Couldn't tell much from the pics, I honestly though it was a chopped up car turned trailer. If I keep it, I will likely do some heavier mods to make it what I'd ultimately like to have. In researching this, I see that the BMW community gets pretty active when one of these surfaces. So, I thought I would reach out to see if someone wanted to try and talk me out of it. The thing works fine, zero body damage - a couple of minor missing pieces - a couple of the tie on's, one reflector, etc. Its a bit dirty, but I'll be resolving that tomorrow. I can tell that the part of the deck that has wood is getting weaker. The only real potential turn off is that there isn't a title. It was supposedly lost. Best I can tell it will be a crap shoot on getting that sorted if that is a major concern.
I'd be looking for about 3k, or to trade for a similar bike trailer, probably something with air shocks, or an enclosed that would work for the same purpose. I'm also taking it to my body guy tomorrow to talk mods, so if there's no major interest in a few days, I'll likely start taking it apart.