Many people post apartments with stock photos, and when you contact them have a fake story about being unable to be there to show you the apartment, then ask you to western union transfer some money — sometimes just to yourself. This ‘proves’ you have payment but by showing them the reciept they can withdraw the money themselves. Often they ask for ID like passport scans then take this info and use it as identity proof to scam the next person.
You also get people who illegally sublet (or legally) asking for a huge deposit and laws here mean you can keep the deposit (kaution) for up to 6 months after people leave. so a constant flow of short sublets can keep people in quite an excess of money that isn’t theirs (it’s often 3 months rent as deposit as standard).
I also hear of a lot of extortionate cleaning fees…you have to return a rented apartment in the exact state (so no room for ‘wear and tear’ ) so german landlords vs ex pats can sometimes be a very unequal relationship in terms of knowledge of rights and what people are expected to do.