[sooheon]

> Collusion can't mean that the sellers all have an implicitly coordinated price.

Why? Obviously explicitly coordinating prices is collusion. Implicitly coordinated prices depends on nobody else defecting to a lower price point. If enough players have a tit-for-tat strategy, sellers can converge to a higher than market price, trivially. This is far from a 'efficient market price' derived from perfect information.