House financially feasible at about 5,000 net?

[...] and have it sent to the owner by the land registry office for €7 per property

No, that just doesn’t make any sense. The market doesn’t work like that.

Is a purchase interest considered a legitimate interest in the sense of the authority to obtain ownership data here?

Just as an example of a bubble price of the type "mainly something". In one of our future neighboring towns, a bungalow was listed for €510,000. Built in 2018, 140 sqm, without a basement, 620 sqm plot (not in a new development area), brick double garage... and still in shell condition. The roof and windows were in place, but the entire interior finishing was missing. In a village in a small community out in the sticks. The thing has meanwhile disappeared from the portals... Someone tell me again about functioning markets. Even if the buyer negotiated the price down, this makes absolutely no sense. He still has to put a lot of money into it.