Backyard dealer, car without TÜV, what’s common?

Hello dear motor talker, I looked at a vehicle, which was a government vehicle until 2 years ago. Until then it was regularly serviced, workshop call: everything great, all wear parts made. But what happened the last 9,000 km and how long it stood around, nobody knows. The dealer offers to have TÜV re-made, if I pay him 100 Eur to prove that I actually have interest. Is this usual?? Does one just rule something like that in writing? I can also I didn’t try it at all, because without TÜV no short-term registration mark, is that right? Up to now I just took a look inside and the engine was started with a start-up aid. However, I can already demand a usable battery, right? Unfortunately, I have no one who can take a professional look at it. Alternative would be a DEKRA visit, but it would also have to be moved first. Would be really grateful for helpful hints!