Tax traps when commissioning foreign construction companies

As a private individual, you couldn't care less what the company does with the VAT. To be sure, however, you have them show you the (German) tax number of the company and check it. If they don't have it or don't show it, stay away.

Why does an Austrian company have to have a German tax number?

A Polish self-employed tiler probably doesn't have one either and is still allowed to legally provide services in Germany, right?

You are not an entrepreneur with an apartment. Unless you have founded a company for it.

And even if you were, as an entrepreneur you are allowed to build a house privately, then you are just a regular consumer.

My link was deleted above.
You can find the site on Google with the following term "Tax traps when hiring a foreign construction company".
It talks about landlords and small businesses. Is that really only related to landlords who do it "full-time"?

Okay, seems to be the case.

Google says:
"The BGH held the view that this landlord is not an entrepreneur because the management of 4 rental units with long-term contracts does not require a planned business operation and he does not need to maintain an office or an organization for the management."

Thanks, that reassures me!

Here, wild things are mixed that have nothing to do with each other.

Asset management or rental and leasing is to be classified in the area of income taxes. There is no (commercial) entrepreneurial status here.

For VAT purposes, however, the intention to generate revenue is decisive for the entrepreneurial status. The services from the rental are therefore already a taxable supply according to §1(1) No. 1 USTG. However, the rental to private individuals is tax-exempt according to §4 No. 12 USTG and cannot be circumvented by the tax option under §9 USTG. As far as I know, zero declarations also had to be submitted in the VAT return in the past. This is to clarify the matter first.

Now to the specific case.
If an entrepreneur from Austria builds in Germany, then for a service under §3a USTG the VAT liability is at the location of the property. So definitely VAT must be paid in Germany. If the client is a VAT entrepreneur, the VAT liability shifts to the recipient of the service according to §13b USTG. If there is no entrepreneur, the company would have to register in Germany. Meanwhile, there is also the OSS procedure to avoid the registration obligation, but I do not know right now if this applies in this specific case.

Now the lessor is also a VAT entrepreneur. Insofar, §13b UST (shift of tax liability) can indeed apply.
I once had in a seminar that a small business owner must pay the VAT when the tax liability shifts or in the case of intra-community acquisition, but cannot claim input tax deduction (because of being a small business owner). I could well imagine that this is also the case for rental and leasing.
Since no tax advice may be given here, I point out that this is a layperson’s opinion and recommend consulting a tax advisor.

A Polish self-employed tiler probably doesn't have that either and is still allowed to legally provide services in Germany, right?

One thing has nothing to do with the other. Tax law is one story. Labor law is a completely different one, and nowadays trade law (HwO) is yet another. If Oleg works for a private individual in Germany, he has to pay VAT here in Germany. How is he supposed to do that without a number? Which also makes clear where the money ends up if there is no tax number.

No, renting out an apartment does not make one an entrepreneur.

§2 para. 1 UStG, feel free to enter "one is an entrepreneur if one rents out a condominium" into any search engine. It is merely a tax-exempt transaction in the case of long-term rental (§ 4 UStG)…please justify opposing opinions and do not just blurt them out.

Found online when searching for the phrase: are landlords entrepreneurs:

Conclusion:
The decisive criterion for whether the landlord is an entrepreneur or not is his commercial activity (§ 14 Building Code), i.e. a certain minimum organizational effort must be necessary for the management of the apartments.

The number of apartments owned by him is not solely decisive. In individual cases, already 2 rented apartments managed by a professional property management can turn a private landlord into an entrepreneur; the BGH has not considered 4 rental units managed by the landlord as sufficient in individual cases. However, the number of apartments is an indicator of entrepreneurial status. The more apartments are to be managed, the more likely it is assumed that there is a higher minimum organizational effort and thus commercial activity of the landlord as an entrepreneur.