I suggest adding a visual indication on the beatmap when it has a custom skin or sound. It's sometimes annoying in multi when the beatmap starts and it has a crappy skin, we have very little time to turn custom skin off and when the beatmap starts it's too late.
Disabling custom skin by default is not the solution because some custom skin are OK and fit well.
Disabling custom skin by default is not the solution because some custom skin are OK and fit well.