Earlier quoted context omitted.
It wouldn't help significantly. People would still get counterfeits when buying from bad sellers.
What? That would help enormously . If they stopped commingling it would be easy to quickly identify and eliminate bad sellers. Consumers would also have the option of sticking to a known-good seller like Amazon and be able to trust that they weren’t going to get some comingled bullshit copy. That’s a pretty damn far cry from the current situation.
You are correct that customers could themselves choose better sellers, but most customers don't care and prefer cheaper over more reliable. That effect is not enough to help "enormously".