What you get out of Gunbot is what you put in. Also, it's not perfect, there are some minor bugs that you have to work around, but all this is easily avoidable with some work and attention to detail. Also, the bot can't predict (no one can) radical swings in the market like what happened when China banned ICO's. My bot was running over night and bought a bunch of falling knives and when I woke up in the morning I had a wallet full of loses. That said, the market recovered over the next two days, so did my bot, and so did my profits.
However... some people don't have the patience for that and end up selling their license. Also, don't expect 2% gains a day consistently and on your entire portfolio. Your bot will make gains on what you give it, but it may not use your entire balance. I'm running with about 25-pairs on a conservative strategy and my bot is typically using only about 1/4 of my BTC balance at any given time.