I think it is fair that the salesman doesn't warn them about any possible consequences. No one can pass responsibility over their own actions.
However, many of the punishments they receive, or rather, the consequences of their actions, have nothing in common with what they were doing wrong. So quite a few end up disappointingly.
Still, the main problem of this anime lies in the fact that the moment you see the characters fall into their own desire's trap there's no reason to be interested in any way about the action. It becomes just a tedious wait for the inevitable ending.
There's no problem with being formulaic, or episodic, but when the formula itself deprives the viewer from any pleasure it's hard to not view this anime as a waste of resources.
