Temporary VAT reduction by 3% until 31.12.2020

This is exactly the question that and I are discussing. Whether he is allowed to do that or not. And that, in turn, has nothing to do with tax law, but with civil law. Hence the suspicion about the many lawsuits that could arise.

A genuinely serious question, since I am not (even remotely) an expert. On what basis should he be allowed to do that? He offers a service. He invoices this service for an amount X. This amount is net; he has to add VAT on top of it. Whether it is 16 or 19 percent is completely irrelevant to him. In the end, he has to pay the same sum to the tax office.

In my administrative law opinion, a company that does not pass on the "saved" VAT but lets the customer pay a possible increase should get a slap on the wrist for violating § 307 of the Building Code. But I am not proficient enough in tax law for that.

Building Code = Civil or private law.
Has nothing to do with tax law (in this case).

A serious question, since I am not an expert (not even remotely).
On what basis should he be able to do that? He offers a service. He invoices that for an amount X. That amount is net, he has to add VAT to it. Whether that is 16 or 19 is completely irrelevant to him. In the end, he has to pay the same amount to the tax office.

That’s also how I personally see it – for me, the reduction of VAT should not come at the expense of the end consumer (or rather, at the profit of the company). I already wrote and explained that above.

But: Musketier’s argument is based on the fact that the offered service always refers to gross prices – if that is the case legally from a civil law perspective, then it would be legitimate not to calculate VAT on the net price but to extract VAT from the gross price.

As I said, if I were an entrepreneur, I would communicate openly. I would not change my gross prices (because it can be an enormous effort) and instead grant x% discount on everything. The customer should be satisfied with that and it would remain profit-neutral for the company. That seems to me the simplest way.

Read this:

Preisangabenverordnung (Preisangabenverordnung)
§ 1 Basic Provisions

(1) Anyone who, in accordance with § 13 of the Civil Code, offers goods or services commercially or on a regular basis to consumers, or who advertises as a supplier of goods or services to consumers including prices, must indicate the prices that are payable including value added tax and other price components (total prices). Insofar as it corresponds to general commercial practice, the sales or service unit and the quality designation to which the prices refer must also be indicated. Reference may be made to the willingness to negotiate on the indicated price if this corresponds to general commercial practice and legal regulations do not oppose it.

Yes, I am with you so far - but the question is whether one is simply allowed to unilaterally increase the net price in already concluded contracts that clearly state net price plus VAT, in order to ultimately arrive at the same gross amount. I do not see that covered by your quote.

I believe we will not be able to solve the problem either. I am not a lawyer.

The question is also whether the government can enforce what it intends with this.
For the hospitality industry, the government lowers the VAT to help the restaurateurs. For the others, it lowers it so the population has more? Must the restaurateur then lower prices by 2% (difference from 7% to 5%) but may keep the difference from 19% to 7%?

Or rather the other way around?

The economy is actually supposed to be stimulated, but the homeowner gets the 3% back and makes his special repayment? And suddenly the money is out of the cycle.

And voilà, the money is out of the cycle.

Why, he has xx more in his pocket every month for the next xx years (calculated, realized with repayment reduction or follow-up financing).