Buyer Centric on it's own may work if the value proposition is strong e.g. Odesk, elance , every Job board under the sun (in some ways), etc.

Bounty based though is intimidating because of the process of defining rates is arbitrary, in a non f2f interaction it's much easier to have a pre-defined set of rules to engage in.

But there is a classic problem of chicken and the egg problem in a buyer-centric marketplace and if one does not think it through, you may be in for a very long haul.