A question is, how would you see evidence of this? Wash trading with Tether has been alleged before but, as far as I'm aware, it's not possible to definitively

A question is, how would you see evidence of this? Wash trading with Tether has been alleged before but, as far as I'm aware, it's not possible to definitively prove or disprove that it occurred. So to me, that's not a strong signal either way, the operation of Tether and their dealings with exchanges are opaque, you need to take what they say on trust, as there are no external auditors.