Fat fingers are mostly a thing of the past. Such a thing is so rare these days as some exchanges have some measures to safeguard the trader but back in the days of exchanges like Etherdelta, it was something to look upon.

If you are thinking arbitrage, then I would advise you to tread carefully. Some of those small exchanges could either be scam or they could be old exchanges that just decided to block withdrawal of some coins indefinitely like HitBTC or Yobit