Terrorists... They kill for a cause (however it may seem ridiculous) and don't care, who they kill as long as it puts them a step closer towards their goal.
If they shoot a trader, let it be read as an act of terrorism. And if not yet hostile, as a casus belli.
Simply, if I were a phantom (hell i won't) I would kill clan traders to disrupt their trade and economy, rid them of income.
Without however demanding fee. just shoot when i'm in range