Entrepreneurs who have received from their subcontractors Freistellungsbescheinigung, i.e. a certificate of registration with the tax office, are exempt from this obligation.

Translation of interesting and important excerpts from the circular of the German Ministry of Finance on the Bauabzugssteuer (construction tax).
The payer's obligation to pay tax even if the tax is of course
undue.

Principal's obligations regarding collection Bauabzugssteuer.
Translation of the BMF-Schreiben vom 27.12.2002
If the withholding has been made incorrectly, the recipient is liable for the amount of tax not paid or paid too low (Section 48a (3) sentence 1 EStG). When the service is provided to a third party (e.g. by insurance companies), the beneficiary (e.g. the aggrieved party) is responsible for the withholding of the tax. Liability is generally independent of the fault of the recipient, if
the recipient has not been presented with a certificate of exemption from the obligation to withhold tax. It is also irrelevant whether the service provider is entitled to secured tax claims in the country. In particular, the recipient may not rely in the proceedings on the fact that the service provided may not be taxed domestically in accordance with the double taxation avoidance agreement.
Pursuant to § 48d para. 1 sentence 1 EStG withholding tax has not been restricted by the treaty on avoidance of double taxation. Claim for
Liability is also possible if the person of the tax debtor is unknown.

The Financial Office decides on its own discretion about bringing the recipient to liability as a tax debtor. In doing so, account should be taken of whether claims exist or may arise in the light of the circumstances of the case
tax.
However, the recipient's liability is excluded if, at the time of the performance, he was presented with a certificate of exemption from the obligation to withhold tax, which he could trust as to its compliance with the law. The recipient is obliged to check the certificate of exemption from the obligation to withhold tax; in particular, he should make sure that the certificate of exemption from the obligation to withhold tax bears the official stamp and includes a security number. Upon submission of a copy of the tax exemption certificate
all data should be legible. There is no obligation to regularly check the tax exemption certificate.

The recipient has the option to obtain confirmation of the validity of the certificate by checking the certificate of exemption from the obligation to withhold tax. If the Federal Finance Office fails to confirm validity or you cannot perform an electronic check, you can be assured by submitting an inquiry to the Tax Office stated on the Withholding Exemption certificate. Failure to submit an electronic inquiry to the Federal Finance Office or an inquiry to the Tax Office is not in itself gross negligence. Responses to inquiries to the Tax Offices in order to confirm the validity of the certificate of exemption from the obligation to withhold tax are provided orally or by telephone. Written confirmation does not actually take place.

The recipient should also not be held responsible if, at the time of the performance of the service, he is not presented with a certificate of exemption from the obligation to withhold tax, he does not make the deduction and a valid certificate of exemption from tax deduction is presented to him at the time of payment.
The trust of the recipient does not deserve protection if the tax exemption certificate was obtained by means of illicit means or false data and the recipient knew it or was not known as a result of gross negligence (§ 48a (3) sentence 3 EStG).
This also applies if the recipient has been provided with a false tax exemption certificate and the recipient has noticed or should have noticed this.

If the conditions for the liability of the recipient within the meaning of § 48a para. 3
EStG, a liability decision or a decision determining the amount of tax pursuant to § 167 para. 1 AO. The relevant decision is issued by the competent Financial Office after hearing the recipient.

Working translation.