i know they did the same thing by making other hunt for them but asking people they don't know is dicc move for the mask guy. at least the MC is close and has work with them few times and know each other.
also Okura properly compensated them with reward items for their hunt while Yamada just make them wear the ring for nothing while tricking them (they didn't know the ring has purpose, MC also didn't go to detail but at least he tell them it does give things he need without taking anything from them).
also if Yamada already pull this move, the fact that he still work with demon and even trying to steal MC magic Stone show how sucks he is at gathering on his own lol