Process of buying property from a private individual - How exactly does it work?

The error actually started much earlier.

You did not make a mistake. Ultimately, no one made a mistake because it happened exactly as intended. You became aware of a building plot through the land registry and asked the owner if he wanted to sell. It could just as well have been that the owner's children had built elsewhere in the meantime, and you motivated the owner to sell the plot by inquiring.

So I don't know which federal state this is about, but in Hesse you can get proof of ownership quite easily sent via Geodaten Online. The reason "rental / lease / purchase interest" can be given there. The rest was then obtained through the residents' registration office.

Both for a fee of around 10 euros each.

Alternatively neighbors or networking in the village. The long-established residents usually know quite well who owns which property. Memberships in fire brigades or other clubs are always helpful in this regard. At least in municipalities with up to around 50,000 inhabitants.

We bought my Exhaus property through a similar action. Saw the property we liked, went to the land registry office and there found two clerks who someone had probably forgotten in the basement :D Two older gentlemen, probably close to retirement, who were very happy when I stopped by! Back then, I got the name and date of birth of the owner and through contacts we were able to locate him and asked if he wanted to sell. He did. Property bought. Maybe it's no longer possible like this today. This whole thing was about 14 years ago now...

So, factually it is such that I cannot just share data we collect for administrative purposes simply because someone wants to find something out. For the purpose of official or police investigations, yes, with a genuine legitimate interest, yes, for example, if a resident notices that an undeveloped area is being used for bulky waste disposal, or similar. Otherwise, it is none of Bürger M.'s business who owns property xy.

It happened to us just like with Wickie - only not 14 years ago, but last month. We looked for overgrown plots in our area and then asked the land registry office for the addresses of the owners of two of these plots - because of purchase interest. We really got the addresses, and one of the owners we wrote to eventually did sell to us. She probably wouldn't have initiated the sale herself, but was happy that now a young family would (hopefully) be happy on her property...

Similar with us: Called the municipality to ask if they have the plots. They didn’t. But the clerk said she heard that someone wants to sell privately and gave us the phone number. Lucky! But that is more the village character of the district with us, even though we belong to the big city. Here everyone really still knows everyone and everyone knows (almost) everything... :-)