Seems from my experience that at least to some degree dang is on top of making sure each person has only one account.
But again, the situation may be different when people intentionally try to do sketchy things. If someone uses separate browser sessions and separate VPN connections then there would not be much HN could do to discover that multiple accounts belong to the same person, except if the person with the accounts made the mistake of displaying voting ring behaviour, i.e. a number of accounts upvoting each other, and that sort of thing
