Construction costs are currently skyrocketing

Yes, where do I start. I would like a company where everyone speaks German for communication. I work from home, we live there, and I want to be able to talk to the people who are with us all day. Then I want to be able to reach someone in case of shoddy work, and without having to cross country borders. And then it is important to me that the people are treated and paid properly.
We might still try MyHammer, although so far we have never found a craftsman with it or at least none that was trustworthy, but maybe it’s worth a try.

Silke got ahead of me with the question or recommendation.
As the saying goes, "Who doesn’t try has already lost." So why so many "prejudices" in your text? ;)
In the end, it is you who decides whether and to whom a contract is awarded. You can set filters on which companies are even considered, read reviews, etc.
I understand that reviews should be taken with caution, but from my point of view, it's still a better option than the "Yellow Pages" without any connection to the executing company.

From my point of view, you have by far not exhausted all possibilities. Even classified ads should be mentioned and sometimes represent a "serious" alternative.

Good luck!

Then I want to be able to hold someone accountable in case of botched work, and that without having to cross national borders. And it is important to me that people are treated properly and paid fairly.

Exactly such companies are also active there.
For us, it was the painting work, once the entire new house.
The description with a time frame was posted on the portal,
about 20-30 responses,
3 local companies came for inspection,
a master company (father + son) executed it.
Quality and time schedule very good.
When asked why they are active on the portal, the answer was that this way they quickly fill their gaps without acquisition and searching, and no one just collects offers.

What is also very helpful are the Facebook groups. There I often see successful requests. At least for painters and gardening work. Alternatively, there is also Blauarbeit. On mydealz, I have experienced everything from botched work to overpriced.

Thank you for your tips. We will now try MyHammer. Then we decided that my husband will try the plumbing. Called this morning and received a callback from the boss half an hour ago. It could be a coincidence, no idea, or not, I don’t want to assume anything. But in any case, he says he will do it this year: underfloor heating and solar thermal, and the connections for the interim kitchen in the basement. He will finish the offer, as he already knows the conditions on site. If we now find a company for the rest, I will be happy.

I have also assigned a few things through MyHammer. Moving, for example. I haven’t had any bad experiences.
For me, it was similar with the energy consultant back then. I didn’t even see him once. I thought that was good, because some have done it more or less on the side and ultimately know less than I do. I preferred to pay the money for the "inspection" and the signature rather than x in-person appointments with possibly poor advice and more money.

@TE: I don’t really understand solar thermal either...

With solar thermal energy, everyone in the area has only good things to report. In combination with the gas heating, it’s a good thing. Whether it pays off, certainly not very quickly, but neither do 30,000 EUR and up for heat pumps and photovoltaics. If we approach this economically, we can simply continue burning gas.