Construction contracts - how reliable are they?

Good day,
my wife and I want to build soon. We already have the plot of land. What we are missing is a construction company. We are looking for a general contractor (GC), whether solid construction or prefabricated houses would not be so important to us. We have already had some negotiations, but unfortunately, these always fail because of the contracts. Now we still have 2 companies in the final selection. A company from Cologne, which is not a GC but a construction cost optimizer (Argus Direktbau) and ID Massivhaus from Hamminkeln. We liked ID's price, but unfortunately, there are no reviews to be found. An acquaintance said we should keep our hands off both contracts because one cannot speak of a fixed price guarantee here, which is important to us.
Now my questions:
How can you find out if a company is reputable if there is nothing on the internet about it?
Is there a way to check the creditworthiness of a company or if it was once insolvent and now operates under a different name?
Should every contract be reviewed by a construction lawyer? In our case, we would quickly lose a lot of money and you do not always immediately know if a lawyer is good.
ID Massivhaus, for example, has no construction and performance description, only a two-page contract. So far, we have only experienced that there were several pages of performance descriptions for each contract. Without a construction performance description, you can’t say what will be installed, or am I wrong?
The contract is also according to the Building Code, but how is it if, for example, ID does not deliver? Can you terminate any contract and then have to pay nothing after a certain time, or does something like that have to be explicitly stated in the contract? What if, for example, no contractual penalties are mentioned, who is liable if the construction is delayed?
And the last question: if you hire a construction cost optimizer, who is similar to an architect, and commissions each trade individually, who is liable if something happens? Normally, a GC must give, for example, a 30-year warranty on the construction and you have only one contact person. But how is it the other way around? Does each trade give the guarantee? But then what is the point of the construction cost optimizer who gives a fixed price guarantee and a multi-page construction performance description? Is something like that even reputable or realistic, precisely because each trade is commissioned individually?
Thanks for the answers.

Then we wanted to build with ID Massivhaus, had almost everything ready, but decided against it. The construction service description is just plain strange.
Now it will be Neesenbau from Dortmund. They have a great contract. Just as it should be.
I believe all three mentioned house builders are low-price providers, but I think it can go either way.
Let's wait and see.

Hello, we started building with Argus one and a half years ago. The construction has significant defects and Argus has seriously miscalculated the costs, so that the house will be around €150,000 more expensive. We cannot finance that. Argus then terminated the contract with us. Due to the flex price option, we will have little chance in court and are now facing financial ruin. I would like to bring this to public attention and have the feeling that other builders with Argus are experiencing the same. Are there any other builders here to exchange experiences with or someone who can give me tips on where to turn to make this public? Something like Bauretter or similar?

We chose the flex price option because we were led to believe that it was still a fixed price, but that discount payments or prices below the calculation would be credited to us in a way that would possibly make more money available for other trades.

We chose the flex price option because we were led to believe that it was still a fixed price, but that discount payments or prices below the calculation would be credited to us in a way that would possibly make more money available for other trades.

We signed a so-called “construction management contract” from Argus Direktbau GmbH.

We deeply regretted it, as building the house with Argus turned out to be a real nightmare from our perspective.

Based on our experiences, we would expressly NOT recommend Argus Direktbau GmbH in Cologne for house construction.