Turnkey fixed price during Corona or cost increase?

receive a "general information"

As long as it is only general information, everything is still fine. It would have been different if you had to sign something else. That would have given the company a free pass...

Then construction delays due to infections would also be mentioned, etc.

They are obliged to provide such information.
At the moment, it is actually not known whether a lockdown will also affect craftsmen.

Are cost increases allowed despite a fixed price without further contractual exceptions?

No, but if they come with that, I would clarify with a construction lawyer what to do.

Our stair builder has now stocked up on wood as a precaution, since the wood market will apparently be almost completely bought up by China and the USA in the coming months.

One then also has to ask why buyers in the USA and China are suddenly so much more liquid than German buyers. The transport price and time are also factors. Getting a container will already be difficult, and the price for it has also risen significantly. The transport price definitely seems to be in the same order of magnitude as the goods. All very strange.

Can you tell me which data from the portals are relevant for the evaluation?

In the balance sheet, that the (equity) capital is on the right side (liabilities) and is as large as possible. On the asset side (left), it should not be dominated only by receivables. It would be good if land and buildings are present in a decent amount.

Look in the commercial register who are the shareholders, managing directors, and possibly authorized signatories.
It would be good if 100% does not belong to one person, and this person is also the only managing director and no one else has power of attorney.
Single-person GmbHs are usually dissolved faster than if several people are involved.

with a BMW or Audi he'll survive too ;)...

That can somehow work if necessary, I know that, I also come from the bottom, had to drive a 5-series for years ...

A general contractor will not build a house at a loss. And it wouldn’t just be one, but estimated at least 10 with a general contractor. If it’s not profitable for them, they establish a second GmbH in advance, close the first one (sale or insolvency), and continue with the second; if necessary, another managing director is installed as a front man. Nowadays there are GmbH "funeral" companies that advertise online and broker corresponding buyers. All personally experienced.

I wouldn’t agree with that. For example, in our hospital network, there is a rehabilitation clinic (yes, a different industry, etc.) that has been making losses for years, if not decades. It is kept alive because: a) fixed costs can be covered with it. These costs remain even if we close it. b) it belongs to the portfolio and one wants to offer the complete package. From ventilation -> rehab.

If the builder now makes losses or no margins, he will not immediately shut down. Because with that he can at least cover the fixed costs and part of his variable costs. Better than looking for a new customer now. Planning phase, etc. takes time.

Now let’s think the other way around. The client loses their job, gets a new one but it pays 10% less. Does the builder say: "We will now reduce the price by 10%"? Just as the client carries a financing risk, the contractor should bear the entrepreneurial risk. And I also assume that if a fixed-price contract is signed, the general contractor secures prices and materials at the latest the next day.

In the balance sheet, the (equity) capital is on the right side (liabilities) and should be as large as possible. On the assets side (left), the side should not be dominated only by receivables. It would be good if land and buildings are present in a decent amount.

Check the commercial register to see who are all shareholders, managing directors, and possibly authorized signatories.
It would be good if 100% does not belong to one person who is also the only managing director and no one else has power of attorney.
Single-person GmbHs are usually dissolved faster than when multiple people are involved.

Thank you, I have looked it up but I still find it difficult to interpret because I don’t know how much is considered “a lot.” The provider we have chosen has equity of about 200,000, receivables of about 250,000, but current assets of 3.3 million. How can I evaluate this now? Unfortunately, I can’t send a PA yet, otherwise I would have asked you directly.