If you opt for a procedure at the Rent Tribunal, they will conduct an independent investigation into the property. They assess the basic rent by means of a scoring system (rental price check). If they come to the same conclusion as we have come to, namely that you are paying too much, they will lower your basic rent. This is binding for the landlord. If you start a procedure within the first six months after signing your lease, this even has retroactive effect! So do not wait too long.