In the US, transactions over $10,000 need to be reported regardless. I don't know laws in Europe, but I would expect they have something similar. Which is to say, you can accept envelopes of cash only for relatively small amounts of money before you are going to get in trouble yourself. The government doesn't like tax fraud, and without the ability to trace things, they can prove tax fraud just because if there was no tax fraud, you wouldn't have a certain amount of money.