You see a newspaper or online ad for a rental. You make an appointment to look at the apartment. You decide to rent it. You make a deposit and get a receipt. A few days later, you notice someone else living in the apartment. You try to find the person who took your deposit. The phone has been disconnected. You come to find out the person who showed you the apartment had no authority to rent it. He simply rented it for a day , and he cheated you.
In a desirable neighborhood, a con man can take 20 deposits in one day. Think about that! Ten deposits at €1500 each, that's €15000, a hefty take for one day's work.
These con men always offer great deals on rent and insist on cash deposits. Beware.