What youre attempting to do is supress facts and information
There is no relevant information. Digging into people's personal affairs, whether on a blockchain or otherwise, may well involve facts, but that doesn't make it any less invasive and inappropriate, especially when no strong or ultimately meaningful conclusions at all are ever reached, only speculation and suggested inferences.
What @steemcleaners is trying to do (and doing) is discouraging arbitrary invasive identity "investigations" which are divisive and create a hostile environment, while recognizing and encouraging the legitimate cases where identity and similar factors matter and are being used to mislead.
So whats going to happen when/if there's a marketplace. Just a revolving door for scammers?
I would imagine it will look a lot like other online marketplaces where people will provide information to establish their trustworthiness (sometimes verifiable, sometimes not), escrow will be used (apparently already exists on the blockchain, though I'm not sure anyone has ever used it), traders are evaluated by those who trade with them for reputation purposes, etc. And ultimately some people will still get scammed, but that is hardly equivalent to a revolving door.
BTW, I don't see anything about a marketplace on the 2017 roadmap so we probably wont be seeing that on steemit.com in 2017 and quite possibly not 2018 either. For now it seems the focus of the steemit.com site is to be mostly for social conversation and fun, not commerce.