as far as I understand it it works like this:
using your example but taking it a bit further
i buy a vote for 3
vote seller receives 2.4 (80%), upvote receives 5ish, smartsteem gets 0.6 as well and that is their 20% profit which they are paying out
so basically they are splitting the profit fully at the moment. Its just worded in a confusing manner
Still no good why would you sell $5ish vote for a $2.4 return. Better self upvote or vote a friend
Right now it costs 70% of the upvote value. However, we'll add the discount soon which is currently about 30% max. The discount gets calculated of the account value of the user.
So by this we give cheaper upvotes to people who don't have a lot of money, but in return vote sellers (and us) receives less.
Yes you could upvote yourself and friends. But selling votes is still more profitable than curation alone.