It's not fool-proof and I still find myself buying only cable brands I trust (I don't mind overpaying for peace of mind when it comes to that). But the likelyhood of fakes (imitations of legitimate brands) is much lower, in my opinion.
eBay could easily fix this in the common case where bulk sales are involved simply by adding a "Show feedback for this item only" feature. But they care even less about providing effective search tools than Amazon does, which is really saying something.
Regardless of the question, the answer from the customer's point of view should involve more transparency rather than less. None of the major online retailers seem to agree, least of all eBay.