Amanda is Spying on Him
This was the repeated message coming from the clans and guilds he already had dealt with. He didn't know that the actual number of mages being infected was much higher than what these clans and guilds asked for.
These clans and guilds weren't ignorant to that, or acting stingy, as the orders coming from their headquarters stated to ask for a small amount of potions first.
Their clans and guilds had already sent very experienced potion masters to analyze this potion, in a try to mimic Arthur's actions and make these potions by themselves.
These clans and guilds suspected that this place was already infected for a long time with this strange toxin, as more mages passed through this place, and all started to show signs of being intoxicated with this mysterious toxin.