While I always found it weird that you can't use Vanguard marks with factions, I just accepted it. Maybe a different vendor to accept that currency may work. Though I do understand why they took the material to crucible marks exchange away. It just doesn't work with the new material for vanguard marks system. I understand that you might not like Crucible, but that's how you get the marks. To be honest, that's the only way you should be able to get the marks. It only makes sense that Crucible marks come from competing in the Crucible.