Arbitrage basically means free money if you have all the right tools. I used to arbitrage sports bets before and I remember being happy with 5% profits. I can tell you that crypto world, like always, is giving much more. All you need to do is keep an eye on stuff.
Poloniex fixed its Siacoin's wallet today and a good opportunity came to arbitrage trade between Bittrex and Polo. I sold my Sia on Polo for 397 satoshis and bought back everything for 365 on Bittrex. It is close to 8% for free. Of course, some of my SC is still confirming on Polo after 3 hours (that stuff is slower than Bitcoin (actually happens)) but I am happy to wait now.
Tip: keep an eye on the markets in all the different exchanges and take opportunities when they arise. Also, take into account the time needed for your funds to be confirmed. Or even better, have some funds in all exchanges for immediate use.
The last thing to note:
It was obvious that SC would be dumped on Polo after the wallet was fixed and people started depositing their cheap SC from Bittrex and other exchanges. For people who are trading short term, it was an easy call.
At the moment I write, there is still around 30 satoshis difference on SC (8% or so) between Polo and Bittrex, so you might want to check it out.
Best case scenario, if you have any SC on Polo and money on Bittrex, just sell your SC on Polo and instantly but back it on Bittrex. Thank me later!