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The closest site to what you're talking about is ooomf.com (They don't have reviews, though)

I'm building a site (CodeDoor) which uses open source contributions as the sole barrier to entry- a nice thing about that is that it self-selects for technical clients.

GroupTalent (http://grouptalent.com) maintains some personal checks on their talent pool. Not sure if they'd be into smaller applications like OP's, though.

Something like this for remote work exist?

That's a big part of what you're paying an agency for. The whole point of elance is diy management.

But not for people who collect code and then find an excuse not to pay, that isn't necessary at all.