I bought a used motorhome in Germany in March last year from Niemoller. It was advertised in mobil.de. I read the reviews about the dealer and they were good. My experience was good at the time. There was no problem with getting temp export plates. The vehicle had valid road test.
I just think dealers don't do due diligence on second had vehicles. If you find a problem they will fix it. The 1 year warranty is in German so I still don't know what it is. Its buyers beware basically. The vehicle had perfect service history and original Hymer warranty checks that made me more comfortable. They took my 1992 Weinsberg for 2k that I was happy to get considering its condition and that it just made it there from Cherbourg in a cloud of smoke.
So back to buyer beware. Know this -motorhomes leak. Old leaks that were stopped and new hidden leaks. So it's best to order rainy weather when you inspect to buy. Ignore any responses to your questions about leak tests or leak inspections. Get in there with a light and sharp screwdriver. inspect and poke every corner, nook and cranny. If something is soft, loose or doesn't look right, it isn't. Loose screws into the walls or roof mean water got in and there's rot.
After a year I finally found the leak in the 2014 hymer I bought. It was the oven flue through the roof, hidden behind a panel so only showed up when the floor got wet a year later. Actually it showed up at the dealer but they said it was the airconditioner and they resealed it. Now of course I am home and have to deal remotely. Hope this helps.