tell them you'll meet them at your work, and you work at the police station ahah lol, we'll see if they still want to do business..
but of course, if you don't want any headaches/hassles, then just don't answer them...
speaking of money laundering, they talked to us about money laundering during a fake money training session at work once. apparently, it's easier to buy for example a REALLLLLY expensive TV from a large store with a lenient return policy and pay cash (the dirty kind), and then go two or three weeks later and ask for a refund, and obviously they won't have 10 or 12k cash, or at least they don't want to admit it even if they were stupid enough to keep that much cash, so you offer to accept a cheque from them..... and now you have a cheque for 10k that you can deposit in your bank account with squeaky clean money.....
i remember our manager told us that if a customer even hinted at wanting a refund in a cheque to say no immediately....