Hello, we had the same problem last year,
our house built in 1998, the buyer commissioned the expert.
We also still had a loan running which the buyer wanted to take over. A well-known notary advised us against it. So we paid off the loan, but with prepayment penalties, however, since our interest rate at the time was 4.6% and with the new financing it was 1.9%, we decided on this option (although the house bank gave us by far the worst offer, so do not fixate on the house bank).
We solved the handover of the house as follows: we were very accommodating to the buyer price-wise (since they will not live in the house themselves but will let it run as a rental property). We can still live in the house rent-free for 1 year from the purchase date, which was set in writing.