Whenever someone wants money from you, you have to be careful. The commission is paid by the person who got the agent. It is illegal for an agent to charge you commission when you have not hired this agent. But if you hire the agent then you need to pay him of course.
Be careful: Never pay money for something you haven’t seen or are not even sure that you will get it. So do not pay money if there is no contract.!
Anyone that wants to get money from you before you hold a lease contract in your hand is doing something illegal.
When looking for a place to live, it is very important that you make sure that you do not fall into the hands of frauds. Be careful by making sure that you have seen the flat before you paying a commission or receiving the key. Do not sign the contract unless you are sure that the contract is serious, if not sure, ask friends and acquaintances.
If you have paid a commission and this is on the rental agreement, the Jobcenter will then contact you and it could be that they will no longer cover your costs (because it would look like that you have enough money available).