What happens when an opportunity arises

The bot uses best bid and best ask of the orderbooks, the best precision available. (Other arbitrage bots use the last price which isn't precise and doesn't mean much for arbitrage).

The downside to this is that taker fees can be higher than maker fees; and that you cannot know in advance at what price you get filled.

The bot takes the real price into account as soon as the market order is filled. Most of the time, the actual P&L of the opportunity is different than the excepted (mostly due to ping delay).

The bot uses best-bid and best-ask prices, but assume that orderbooks are liquid enough to fill all your money on those best bid/ask prices. If you run the bot with enough money to move the prices, or on relatively empty orderbooks, you might have unexcepted slippage resulting in an actual P&L being smaller than the excepted.

An option that will use limit orders instead of market orders, taking into account the quantities available at each bid/ask price, will soon be available.

Logs of the Barbotine arbitrage bot showing a difference between excepted and actual P&L