Indeed, cloners will find ways to flood the market, because that's the effective way.
As someone who likes to discuss about solutions, time is something the cloners do not have. They are always trying to clone the currently trending things, so they cannot wait for three months or so for the trend to die out.
I would say a mandatory 3 month period of closed beta would help cull many bad actors, with strict requirements as what would suffice. Valve could in the meanwhile scan in case the assets are stolen from another games listed in their store.