>In a search for "designer sunglasses", a reputable site is more relevant than a scam site.

No it's not. That search term is very open and does not indicate at all that the searcher is looking for reputable sites. A search for "good designer sunglasses store" then maybe. I think you're mixing up the job of a search engine and a review site.

Google appears to disagree with you, as their recent modifications to address this issue have shown.