Selling a car – how’s it going?

Hey together, wants to sell our old car. Thought I’d put it in on eBay classifieds because it doesn’t cost anything. It’s an old Getz with about 190,000 km. How does it work if an interested person wants to register and buy the car. At the moment he’s still registered. Do I have to log it off before the buyer can register it again? Can the new buyer re-register it and is that certain for me? I don’t want anyone to re-register the car properly and then I’m on the E-mail. How should I best proceed? Thank you for your help!