These marketplaces share a lot of core business similarities to that of the daily deal market as early as four year ago, no? At scale (depending upon which niche you choose for your site) will require money in to make "money out". No one in this thread seems to be highlighting this with the exception of those sites listed, little VC dollars have been invested thus far.

It's a serious question and one that's not secret sauce, I'd argue. The execution of your business and that of any sticky viral hooks you can build in will leave you at the winner's circle years from now.