Use the price difference between some exchanges:

\- Current buy rate at Bittrex: $3640

\- Current sell rate at BTC-A-Trade: $4020


Steps:


1. couple days ago I've sold  10 bitcoins at BTC-A-Trade and I got $44K payout.
2. then a bit later I bought the same amount of bitcoins for $40K at Bittrex,
3. = which leaves me with $4000 profit.



The same can be done on any other two exchanges if the margin is similar to this one.