Use of Credit vs. Equity

He pays 1250. He thinks he has to pay 1500 for a new rental.

What is the better alternative to buying given the overall scenario; certainly not leaving the money in the bank, right? :)

With the current interest rates, builders from 10 years ago who calculated with tight budgets and had low repayments must have been almost forced to sell. I would continue paying the rent now and start the search for a house without time pressure.

With the current interest rates, builders from 10 years ago who calculated tightly and had low repayments would almost be forced to sell.
I would keep paying the rent now and approach the search for a house without time pressure.

Ten years ago, the interest rate was about as high as it is now. If the repayment was too low, then the monthly burden changes little. That is why no one will sell.

At the current interest rates, builders from 10 years ago who had calculated narrowly and had a low repayment rate would almost have been forced to sell.

The prices 10 years ago were completely different. Accordingly, the residual debt is relatively low.

Have you ever tried to find something "quickly" in Stuttgart? ;)

So your future million-euro project exists only in your mind and nothing concrete has been done yet? Then I would exclude that from consideration.

Otherwise, the increase in the value of the property itself should also be taken into account; according to 3 appraisals, the value is already significantly above the discussed selling price, so at resale the risk of loss should at least be limited – yes, unless the market crashes – but that can also happen in the stock market...

The mere number of appraisals would make me suspicious. Nobody gets 3 appraisals just to sell something. And on top of that, your landlord is then selling "significantly" below the determined value. He’s certainly 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.

Get the minutes of the owners' meeting in advance to see if there is already something expensive in the pipeline. Or simply ask: Why does the seller want to sell?

With the current interest rates, builders from 10 years ago who had calculated tightly and had low repayment would almost have been forced to sell.

The interest rates with a 10-year fixed term in 2012 were between 2.5 and 3%, so at a similar level as today.
Last year was the year for extensions. 10-year fixed terms were available in 2011 for 4%, last year's follow-up interest rates were a joke and have shortened some terms up to the final repayment by several years at the same rate,