How can you avoid this unanticipated surprise? Margin calls can be effectively avoided by carefully monitoring your account balance on a regular basis, and by using stop-loss orders on every position to minimise the risk. Another smart action to consider is to implement risk management within your trading. By managing your the potential risks effectively, you will be more aware of them, and you should also be able to anticipate them and potentially avoid them altogether.
This is a very large question, as many important factors other than Forex robots influence your trading profits, the first and most important of them is yourself and how self confident you are, your available investment capital, the broker you are trading with, the currency pairs you prefer to trade, the market conditions while trading and finally the Forex robot you would choose! While a good Forex Robot can limit those factors bad effects on your profits or even abolish them, no one can predict exactly how much you can gain!