Please don't get arbtrage confused with these 'guarenteed get rich' quick schemes. You don't always make money no matter which way the price moves, it has nothing to do with the direction of price movement.
With arbitrage, you should always make money on each of your trades. If you do not then you are doing something wrong (likely holding onto your bitcoin position for too long).
What could prevent you from profiting is the lack of trading opportunities.
+1
It should be foolproof, at least in theory. Regarding opportunities, with new exchanges popping out every day, there is always something to trade. I cannot find lots of depth, but there are always opportunities.
You should not necessarily be trusting new exchanges like this. You will always have the chance that an exchange is going to run away with customer money (this is especially a threat with newer exchanges that have little reputation because they have a lesser steady flow of income from trading fees)