Have there been any buyer-centric, bounty-based services that worked?

Taskrabbit and oDesk.

Though over time the most common requests are usually standardized into products to reduce complexity for the buyer. For most buyers the open ended nature of a bounty system is intimidating.

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.

A big (maybe biggest) reason why buyer initiated bounty markets don't work is that the buyer is shouldering the initial cost and risk. They have to take the effort to *maybe* get a result, when they're the one trying to spend money and want to be as lazy as possible.

In contrast, if they go to a seller-driven market ("I will sell this for $50") then they know those opportunities are ready for their taking.

The markets where this works are the ones where the demand-supply balance is so wonky and/or so liquid that a buyer is sure to get responses from sellers. Examples would be oDesk/elance/99 Designs, where people post "I want to pay $100 for xyz."

You could count the stock markets too if you include bid-ask systems.

Please check out: https://www.articleonepartners.com/

It is a crowdsourced platform to help locate prior art for patents, which is generally used by patent attorneys to try to invalidate patents.