I agree that the word knowingly needs to at least be inferred. This is called mens rea, which is latin for "guilty mind". It is a common principal in legal systems derived from english common law, and basicly requires intent to commit the infraction that is accused. There is a difference between a vendor who sells a AEF infested acro knowing that it is infested, and one who sells an AEF infested acro without knowing that it is infested.
There is some talk of dispute resolution. I would reccomend that the mods stay away from dispute resolution as it can become a sticky area. Leave all dispute resolution, to the "feed back" function, and expressly state in the vendor rules that being a vendor on this forum is a privlidge that can be revoked at the discretion of the moderators, and that the vendor agreement contain a "forum clause", that requires all disputes between vendors and MR to be handled in a specific venue such as the IFCC.
Furthermore, I would require all vendors to hold harmless MR, its moderators and members for negative feedback that is left. You don't want a libel suit, because someone trashed a vendor.