“After carrying out the order, the Mietwagen must return to its base without delay, unless it received a new order from its base or the operator's home before the trip, or during the trip.”
That is the Rückkehrpflicht, the return-to-base rule of the German Passenger Transport Act (PBefG). You must also record the receipt of every order at your base, on paper or electronically, apps included, and keep the record for one year.
The BGH: you are liable for subcontractors too
On 3 June 2026, the Bundesgerichtshof (BGH, Germany's Federal Court of Justice, case I ZR 123/25) upheld a Cologne taxi cooperative's injunction against a company running Uber X trips with Mietwagen. A subcontractor's car had waited at Breslauer Platz after dropping off a passenger. The company is liable under § 8(2) of the Unfair Competition Act (UWG).
BGH press release no. 100/2026 · Source (German)
The rule matters in Berlin as well: according to the Senate, the courts confirmed breaches of the Rückkehrpflicht, missing company bases and insufficient financial capacity as grounds for the LABO's rejection decisions.
Berlin Senate press release, 11 April 2025 · Source (German)