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A lot of. There are bots even with posts. @donaldtrump is @steemed's bot, i am almost sure, but there are posts, one even with 1000+ reward.
And There are Huge bot-owners, like @nyt (149+ found bots) and even GIANT bot-owners like @angel (668 found bots). And it is only top of iceberg, everyone could look at here on blockchain frontend called steemit.com If You look at blockchain itself - there are a lot of very interesting information about early adopters and their real piece in steemit.

Is there a way to reliably find which accounts are bots and which ones aren't?

I can not to say with 100% guarante, but, look at accounts, for example @vitol, @shell, @glencore, @ford, @ethereum, @sex, almost all of them have no one post\comment\reward and withdrawed Steem to @steemed. They are bots with one aim - to be sold. And there are accounts, owners of wich are invisible for me. @unix for example costs 34000$+, @microsoft 69000$+

Ah, interesting. Account name squatters. Will be quite interesting to see how this developers. Seems we should start tracking this stuff now while the network is still small... but at the same time many value their privacy and don't want their identity known. I have mixed feelings about that since this is a "social" network after all.

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