If Amazon can get sued every time someone burns themselves with a knockoff product, I would think their incentives would shift from:
"Pay as little as possible for quality assurance, down to a floor of $0"
to
"Pay as little as possible for quality assurance, down to a floor of $whatever number would convince a court that we made a good faith effort to prevent knockoffs."
At least, it incentivizes Amazon to chase the culprits. The question is whether that incentive is big enough for them to fix / improve things.