This must be true for most financial activities. But since I’m receiving something like 5 emails per day from random people  who wants to run my bitcoin-arbitrage tool, most of the time I’m replying with some warnings:
Can you trust the exchanges ? The answer is NO, you can’t:
Trade engine can be laggy (up to 1 hour lag).
APIs are buggy. get-order-book replying with 2 hours delay is unacceptable. some API function doesn’t work time to time
Bad “cloudflare” config sometimes blocks normal API calls (Yes, I’m looking at you bitstamp)
The site closes but a part of API is still working (Yes, i’m looking at you bitcoin24)
And the worst thing: they can close at every moment and block your money (1 hour to infinity). History prove this one, see what happened to Bitcoinica, Bitfloor, Bitcoin24, Bitcoin-Central. Who’s next ?
Can you trust tools ? Of course NO. If you can’t read code (blind, not a developer or closed source), don’t use the tool. A malicious dev can steal your money so easily.
To trade you need money, fiat AND bitcoin. If you don’t have bitcoins, are you ready to buy some ? Yes, risks everywhere !
Moving fiat is so long… SEPA transfers ? sure let me wait a week (I’m wondering why it’s so slow, do banks have computers ?). That means you’ll need A BUNCH of money (fiat AND bitcoin) in every exchanges you’re trading on. Then balance them time to time when they drift. And that opens a big risk if one exchange closes and blocks your money.
So yes, Bitcoin arbitrage seems easy and very lucrative, but it’s very risky. Not because of arbitrage principle itself, but mainly because you can’t trust exchanges.