This is the thing that really annoys me. It doesn't seem that technically difficult (aside from the migration pain) that recognizes product:seller as a primary key, rather than just product.

They're already swimming in reviews. So I can't see them not getting more than they're losing by empowering customers to torpedo bad sellers.

Of course, this would also mean fundamentally changing their logistic practice, which is probably why they aren't interested in doing it.