For some of these bots, the user can program them to buy at predefined low and sell at a predefined high. I’m pretty skeptical about this maybe out of ignorance or just sheer human skepticism for stuff like this. Have you ever used a bot to automate your trading? Do you trust it enough to make the right decisions? If trading bots are as good as they claim, why are folks not using them as much as they should?
You can program to buy or sell at anywhere in predefined manner but after you buy, there will be no guarantee for the market for not falling down further 
. I mean trading bots are not about simply buying or selling at predefined levels but at trend changing points which may not be available well in advance to anyone hence we need to go for technical analysis. Technical analysis is a kind of sea sized monster and no one could cover it completely in coding. So, basically trading bots are half-baked bread which looks good for some people but most people find it bitter.