It's completely true that if the guys are in relationships, sales go down and fans retaliate. Oftentimes, the female fans will turn on the supposed or real girlfriend of their favorite guy and purposely spread really nasty rumors all over the net. The same can be said for male fans of female stars. This is a big reason why Ayumi & Nagase never talked publicly about their relationship because there's no telling how fans of either of them would react.