However, if they are themselves scammers (e.g. refuse to pay out jackpots or anything to that effect), then cheating on them can be morally justified (as I see it)
Yep, something I had in my mind for discussion too at a later point. Like does scamming a scammer make you a scammer yourself ? From the general answers so far in this thread, I would assume that most users would be ok with doing it and you are no scammer per se, more like a modern Robin Hood maybe. But then again, a lot of users showed high moral standards (which is good) and even scamming a scammer is not easy to square with your conscience. You either have it kind of in your DNA or not imo and feel bad for doing it yourself, no matter the circumstances. Technically it will be hard anyway, since they are pro with scamming most of the times and you are not.