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tell me a little more about them, why are people selling votes if they can just farm the 90% curation posts? is it something to do with their curation curve?

what other economic parameters do they have? free downvotes? what's their reward curve?

what's the overall economy there like?

Most of parameters there could be changed by witnesses without any hardfork.
By now the majority of top-witnesses have voted for linear rewards and zero minutes early voting penalty.
The actual consensus state can be viewed on explorer https://explorer.golos.io
My understanding why people are still bying votes is some sort of addiction to be on the Trending.
And actually it isn't always 50/90, because vitnesses votes are "split" between something like 25/75, 50/50 and 25/90, consequently the parameters can change a few times a day depending of who from the reserve witnesses is taken into the calculation.

I see

Then I disagree strongly with linear rewards and no curation auction window and full priced downvotes

I somewhat disagree with a curation slider too

Putting these all together, I'm not at all surprised at their economic failure

I don't think this economic failure have anything to do with the curation model.
And actually the failure of falling from $0.30 to $0.05 as it's the case of Golos isn't so much different to falling from $6.00 to $0.3 as it's for Steem.

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