Purchase opportunity single-family house from the 80s - risk?!

Apart from the location, many things are not described. For example, the windows and doors, insulation of the roof and facade. Extent of the electrics, etc. etc... It may be that the windows still have a U-value of 3.0, are drafty, and the roof is insulated with 8cm of brittle glass wool. Then it will indeed require a renovation.

If the house was worth 600,000 last year, then it is still worth that this year.

I don't believe that. New listings still come in at old prices and after 2 months the price then goes down. The 1-2 remaining interested parties now have no pressure. When we were looking 2 years ago, you had to commit at the viewing and offer more than the asking price. Now you have time to think, and if the seller does not want the price, you just wait until the next house comes along soon. It’s also clear, the prices (honestly calculated as purchase price + interest) have simply increased incredibly over the last 12 months. We have now reached the peak in that respect and it’s going down a bit. How far... no idea. And I would currently put even less stock in an appraisal than usual. The parameters involved are simply too volatile right now, you can come to completely different results even with valid assumptions. Consider a budget and bid accordingly. If it doesn’t work... more opportunities will come in the next months.

We would have liked to act immediately, but unfortunately the heir has now commissioned brokers to evaluate the property (however, the heir wants to give us priority after the evaluation to purchase without a broker),

He has commissioned the brokers to provide a free assessment. However, they have not been given the mandate to market the property. (you can think whatever you want)

Value lies in the eye of the beholder (or as they say in the local dialect: Wääd is, wat ene Jeck doför jitt). Personally, I consider a price estimate by a broker as an acquisition tool to be even more worthless for the seller than broker mustard in general – but if the seller wants to believe in it, you will have to live with that. The risk of incompetent advice resulting in a price too high for you is the same as if the seller conducted a spontaneous survey in the pedestrian zone. However, if the broker also gets the marketing mandate, I see your chances of acquiring commission-free as close to zero. Be glad if you have only one single heir (or a community that authorizes one person alone to speak for all). That way the worst obstacles are already avoided, and you can also get past the broker then.

If the house was worth 600,000.-- last year, then it still is this year. The chances of finding someone who will pay 650,000.-- have clearly decreased, but it's enough if 2 out of the 50 interested parties from last year remain.

I don't believe that. New listings still come in at old prices and after 2 months the price goes down. The 1-2 interested parties who remain now no longer feel pressured. When we searched 2 years ago, you had to commit at the viewing and offer more than the asking price.

You are both probably right - overall this means for the OP that the risk of a price increase is probably low, but the risk of time passing until the seller possibly returns to a realistic price is all the higher. In short, an agent is always a risk factor - just unfortunately one that the OP can hardly influence. Unless he makes the seller a hard-nosed offer, but many interested parties are too emotional for that.

We haven't had completely bad experiences with real estate agents. Two of them actually valued properties quite realistically (not cheap, but not overpriced either). So, don’t let your head hang and wait for what the seller says. Alternatively, run the house through valuation tools or have it done by your financial broker (if available).

He has commissioned the brokers to provide a free appraisal. However, they are not given the order to market the property. (You can think whatever you want)

Is that so? I would just say: He can tell you a lot of things!

As stated, we fear that the brokers will set an "old price" to get the assignment...

I will try to convince the seller (if the broker suggests a price that is too high) to reduce the price. That is the plan

Of course, that can happen. But why should the seller sell to you for less if he is promised €50,000 more? The market still determines the prices. And he has every right to gauge the market value.

What is very likely to happen is that the seller will keep you hanging with warm words, that you will get the house if no one else takes it for the €50k more.