Fair disclosure: I am angel investor in a company called Survata which allows companies to access market research via a self-service web application.

I don't think a marketplace of market research freelancers is really filling a significant need or pain-point. Companies care about getting access to data, and generally have someone on staff or sub-out professional assistance if required.

I recognize this doesn't answer your question directly but as it seems you are trying to determine the viability of the concept, I am answering it in that context.