Price increase after order confirmation / contract conclusion

It’s not a general contractor, but a single trade. Everything is still fine with the other trades - luckily.
We don’t want to terminate in the first step, but the legal situation would still be interesting.
What “annoys” me: if the prices went down, he would pocket the amount as well. But I also can’t do anything if it’s not already ordered or if the prices go up.

Of course, it could be that this trade is blocking all the others in execution. A stupid starting position.

Was in the specialist building material store yesterday. They don’t ask about price anymore but order like crazy. Also a huge queue at the pickup. Everyone wants to make it nice for themselves. Everyone has time.

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We do not want to cancel in the first step, but I would still be interested in the legal situation.
What "annoys" me: if the prices were to go down, he would pocket the amount as well.
...

The same questions arise with the current negative interest rates, i.e., custody fees.

Are the General Terms and Conditions valid according to the contract? That might be stated in there.
If it only "annoys" you that you would not benefit from falling prices, suggest a sliding price agreement.

Muster inspections will mean the strictest discipline, and possibly some cunning.

Could you please elaborate on this, as I also have concerns about this point in our construction?

I see it the same way as 11ant. The service provider will not be happy about the initial quarrel and will not want to be left with the additional costs. Therefore, it is obvious that they base any additional charges on a particularly favorable surcharge calculation for themselves. If mutual fairness in cooperation is assumed, rather than a "your own fault" principle, both construction partners act differently and mutually ensure satisfaction and results. I find "give and take" better than "everyone takes what they can." Both require a framework. Of course, I know that I am increasingly called naive for this. I manage quite well with it.

Someone combined their entrepreneurial risk with stupidity.

You made my day :D It is still unclear which trade or order volume is involved. For a stair builder, the additional cost and volume will be different than for a bricklayer. Depending on when the trade starts, one should also be able to inquire about potential additional costs. I would not sign a blank check in the form of the contract addition.