How can I make sure the car is logged out?

Hello Unfortunately we have to separate ourselves from our Astra F. First I wanted to give it away, since he has no TÜV anymore from Wednesday, but then I thought that I might still get a few euros. I have it now at ebay classified ads and already a few interested parties who pay up to 550€. One also writes quite clearly “Export”. But how can I be sure that the car is also logged out? Is there a clause in a purchase contract? Online registration funk It is not allowed since before 2015, but today it is used again on Monday and can then be picked up from tomorrow. Do I still get this regulated in one day? I have never done this before and therefore have no idea what I have to pay attention to. Perhaps there is someone here who knows each other. If important: The car is registered in Hesse in the district of Groß-Gerau. Thanks for your help Roland