I know it's hard, but other sites have dealt with this too. I do wonder if all accounts should have to be paid for. Even a few dollars would deter such behaviour. I know that's an obstacle to poorer people, but Steemit could get overrun with such 'sock-puppets'. I just don't have the answers for this.
I'll probably discuss this with folk at Steemfest. It's an important topic
I think the proposed change in HF20 does have some potential by creating new accounts with zero voting power but a minimum allocated bandwidth without available stake instead.
At least this does take the incentive out of mass creating new accounts, but I am certain it also opens up some new exploits of its own!
I think there is plenty alternatives to charging people. The would deter most new users.