Speaking as someone from another country, lawyers have been used in the past as a way to move/launder money because of confidentially, and how much money can move through a law firm without suspicion.
In most places, lawyers have a certain amount of cash-money that they are allowed to take from a client.
This often isn't a law of the country, but a rule of the "law society" which controls who is allowed to practise law.
Also, does some form of "legal aid" not exist in Belgium?