Real estate purchase agreements must be notarised in order to be valid (Section 311b of the German Civil Code (BGB)). A power of attorney for such a transaction must therefore also be notarised or at least publicly certified in order to be effective. If someone (usually the real estate agent) acts with a verbal power of attorney that has not been notarised, he/she is acting as an unauthorised representative from a legal perspective.

In practice, the unauthorised representative often represents sellers or buyers living abroad. He signs the purchase agreement, which is initially provisionally invalid until the represented person gives the approval. This must be done in the form prescribed for the property purchase agreement, i.e. also notarised. The agreement becomes retroactively effective with the notarial approval.