If these bots works as they claim, why would they be selling it rather than using it themselves? It would make more sense for them to just run it and keep it a secret right? Also these bots do promise for profits so I'm not too sure yet.
What you just wrote is precisely why the ones that are being sold are not the ones that the developers would actually use. One you start listing an item on the market, you're opening it up to heavy saturation.
The opportunity to scam someone is always there, as well, but this happens in nearly every situation.