I've looked for arbitrages manually, and used to do quite a bit of arbitrage betting. It isn't that hard to find considering there aren't any public bitcoin sportsbook scrapers out there, so it can be quite profitable. I have done probably near 20 BTC volume from arbitrage betting, and netted over 0.3BTC. It can be very profitable, but a mistake could cost you. I lost around 0.1BTC from my first arb because cloudbet showed a market, and the limit, but it wouldn't accept any bets on it.
What tools you use if its no secret? or you just look for directly on bookies? if this true i dont understand how do this without spend a lot of times