If u have the quest Seek Out Brother Tosai given to u by Bujo (in Kaineng Center)[also given by Ke Feng/Senjo Wah in the Undercity] in your Quest Log the Am Fah will NOT attack you in Wajjun Bazaar on your way to the Undercity.
This is also useful
>When you want to VANQUISH Wajjun Bazaar (as u will have less enemies, as no Am Fah at ALL in the entire explorable area of Wajjun Bazaar will be hostile, and thus it will be faster)
>If you are doing the Zaishen Bounties for Chung, the Attuned or Baubao Wavewrath.
>Any time u need to go to the Undercity (such as when doing "When Kappa Attack" during Winds of Change)
And thus i recommend NEVER doing this quest but ALWAYS keeping it in your Quest Log.