As a legendary blacksmith I have been creating artifacts of great power - armaments that make warriors almost invincible.
As a proper patriot I have put several sets of these magical armors on guild store so that noble warriors of my alliance could buy them for a modest fee that barely covers my costs.
Can you imagine that this sneaky, treacherous, covetous merchant that my guild has hired, sold one piece of this finest armor to a member of enemy alliance?!
It must have been procured by a spy so that my blacksmithing and enchanting methods could be backward engineered to the detriment of my alliance!
We need faction locks on guild traders so that this treachery could never happen again and my powerfull artifacts wouldn't be used against my people!