Errrmm... Those services that are us-based will cut him off quickly due to FINCEN regulations in the US for being a money transmitter. Not a good route to follow because again, you're trusting someone who may have a shady past, etc.  The centralized exchanges have been terrible, especially those overseas... Mycoin just stole over $300 million.

I think a better idea to back is the decentralized exchange, https://bitsquare.io/

In general, being an "exchange" centralized or decentralized can be trouble if you are in the united states, you should review Section 5330 of Title 31, United States Code if you're in the US.