Which is what this boils down to. Ross didn't know what people were selling. Could be pure high-quality stuff, could be contaminated stuff, could be stuff that was cut up with fent. He made money either way.
Drug producers want pure products. It's almost entirely middlemen who cut drugs with whatever random chemicals they have on hand.
Based on what? This sounds completely made up. Anyone could sell on Silk Road, and faking reviews would be trivial on an anonymous platform. And if someone died from drugs they bought, they're not exactly leaving a review, are they?
Sellers have reputations in real life, but it can actually be difficult to link a death to a specific dealer without a thorough investigation. Even more so on an anonymous platform. Would Silk Road have cared if the police linked deaths to a specific seller? Fuck no.
For the record, I am not anti Silk Road, I'm actually for legalizing drugs. I just find the notion that drugs online were inherently cleaner to be naive Libertarian propaganda.