They may ask where you got your money from but that's usually it and a vague answer is enough like "it was used for payment of services in 2012" or "I've been day-trading for the past two years on so-and-so exchange". As long as there's nothing fishy about your answer, they'll do business with you. If/when law enforcement comes asking, they'll provide your answer about source of funds. If you lied to them, THEN you get in trouble with law enforcement.