Use of Credit vs. Equity

According to 3 expert reports, the value is currently significantly above the discussed sale price

Just a tip for understanding the expert reports (why three?): The one who commissions the report also determines the result. I would only trust an expert report I commissioned myself, where the expert is supposed to evaluate independently. It’s about the same as when buying a kitchen or furniture from you. Write an incredibly high price on it and give 80% discount. The buyer is thrilled and the seller also makes the deal of a lifetime...

Does the current market interest rate factor into the appraisal? A 6-month-old appraisal is already completely worthless given the current interest rate developments. Sorry, but this all smells fishy: Much less rent than possible, much cheaper purchase price than market value... classic methods to push an overpriced apartment onto uninformed first-time landlords. It doesn't have to be that way, but unfortunately it sounds like it.

Does the current market interest rate factor into the appraisal?

It has no place in a tangible asset appraisal.

It is quite logical that if the lease has been in place for a longer time, the current rent is not applied but the rent is significantly lower. Nothing unusual about that. It is also not uncommon for several appraisals to be produced when you want to sell a property and talk to different real estate agents.

Likewise, most additional costs, such as property tax mentioned here, are fully transferable. So they can be deducted. Since you are talking about a five-figure net income monthly, the rental alone makes sense for you from a tax perspective. If necessary, you can run part of the financing for your planned new owner-occupied building through the apartment and then also claim the interest for tax purposes.

It is not unusual for several appraisals to be made when you want to sell a property

Yes, it is. And even more unusual that as a seller you immediately present three (!) appraisals, all of which end up higher than the desired purchase price. Each appraisal costs a four-figure amount – and you do that to do the buyer a favor and also significantly come down on the price? Why do that? Because you're a do-gooder and money doesn't matter?

Just the number of appraisals alone would make me suspicious. No one gets 3 appraisals to sell something. And on top of that, your landlord then sells "significantly" below the determined value. He must be giving away tens of thousands of euros...
Do you actually understand specifically what the appraisals evaluate? Like how the appraisers assess the individual aspects and arrive at their figures? When a floor covering is considered like new. And so on.

I had the appraisals made, see below.

Yes, it is. And even more unusual that as a seller you directly wave three (!) appraisals, all of which come out better than the desired purchase price. Each appraisal costs a four-figure amount – and then you do that to do something good for the buyer and also come significantly towards him in terms of price?
Why do that? Because you’re a do-gooder and money doesn’t matter?

No, at least there is nothing unusual about that.
It was interpreted that the seller had obtained 3 appraisals; but that is not the case – he only had one.
The other two I had made myself to validate his.
The appraisals did not cost a four-figure amount.

And regarding the question why it is being sold, there is also a verifiable logical reason: serious illness and now a need for money for a new building suitable for illness and seniors.

So at least I cannot see any absolute malice here; a lot has been negatively interpreted...