I also agree that it's still not particularly great, but I have noticed a pretty substantial improvement in quality. The fundamental problem here is that retail is a huge, huge mess. With exceptions for innovators like Walmart, most stores don't know what they have on their shelves, when they're out of stock, when something is purchased...it's absolutely absurd. The quality of the data is simply never going to be as good as Amazon's, charging for product listing ads is one of the way that Google is trying to nudge incentives towards higher quality data.