Real estate sale - Equipment and apartment separate?

A little update at this point:

The buyer was not even remotely willing to agree to the following options:

1. Inclusion in the notary contract
2. Payment in advance
3. Payment into an escrow account with the broker until the notary signing

End of the story? We said we absolutely would not agree to a payment after the notary appointment, under these circumstances he does not want to sign the purchase contract. He says, okay then I don't want to anymore xD
So, tough luck. The next ones are already waiting at the door.

Good decision, the trouble would probably have come!!!

I also suspect that there would have been trouble, did everything right.

Good decision

Definitely! The buyer had really made an effort beforehand. Wanted this and that, incredibly many details. Mind you, after(!) the offer was submitted. At some point, the feeling developed for us and the realtor that he suspected someone behind every bush trying to pull a fast one on him. We could already see that he would cause trouble over every little thing later on. Possibly it’s because he is a well-earning young (really young person) who was supposed to be financed by dad. No idea. The fact is, we were in the bidding process. The buyer made the highest offer. Now we have set a fixed price that is above the bid. And the first interested parties have already come after one day. Apparently everything was done really right.

End of the story? We said we would under no circumstances agree to payment after the notary appointment, under these conditions he does not want to conclude the purchase contract. He says, ok then I don't want to anymore xD

Good decision on your part. To me, that clearly sounds like he had fraudulent intentions. No "normal" person would give up their desired property for that reason, especially since you offered him enough alternatives. Great that you didn't fall for him.