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

Focus on the more difficult side of the marketplace. For instance, if you think it'll be easier to get suppliers, then focus first on getting buyers - always be working on your toughest problem (aka your biggest risk). You'll find some great blogging on Marketplace and Platform topics here http://platformed.info (read the ebook too!)

Check out https://www.balancedpayments.com/ They are made for marketplaces. Airbnb CEO among others invested in them and they have some of the best pricing/payout fees. Also some good info on http://www.collaborativeconsumption.com/2013/10/08/online-marketplaces-are-hard/ One of Balanced Payments co-founders is writing this blog series on marketplaces.

It depends on a number of factors but I'd boil it down to two key things to start: 1) What is your real cost to provide a free plan or trial? 2) Who exactly is your customer and what are they used to paying and who and how do they pay today? When you say "online workforce marketplace" it sounds as though you're placing virtual workers. If that's the case, or if you're paying for the supply side of the marketplace, the question is how much can you subsidize demand? Depending on where you're at in the process, I'd also question how much you can learn about the viability of your marketplace by offering a free version, assuming again, that free is actually a real cost to you. I was part of a SaaS project that started charging people for early access based mostly on just a good landing page (we clearly stated they were pre-paying) and were amazed at the response. I've also run a SaaS product that offered free trials and realized that the support costs and hand-holding and selling required to convert from free trial to paid wasn't worth it, this despite the product's significant average ARR. You might be better off providing a "more information" sign-up form (to capture more leads) and let them ask for a free trial while only showing your paid options. I've been amazed at the lead capture potential from a simple "have questions? Click here and we'll contact you" This is all the generalized advice I can offer based on the limited information I have, but happy to dive-in further if you'd like on a call.

For me personally, no. However, what you really need is a larger data set. Gumroad just did a post on prices ending in "9": http://blog.gumroad.com/post/64417917582/a-penny-saved-psychological-pricing 37signals started with prices that ended in 9: http://37signals.com/svn/posts/1287-ask-37signals-how-did-you-come-up-with-pricing-for-your-products ... but they later did research and found it didn't matter (for them). The answer for YOU will likely be to test these things for yourself on your SaaS app.

It's very important. (first, read this article by Josh Breinlinger - http://acrowdedspace.com/post/47647912203/a-critical-but-ignored-metric-for-marketplaces) The way you achieve success in a marketplace is by driving liquidity for both your supply & demand. Demand-side Liquidity = When users come to your marketplace, they can achieve their goals. Supply-side Liquidity = When supply comes to your marketplace they can achieve their goals... which are almost always to make money. If you're making a large amount of your supply-side users a full-time income, then you're helping them achieve liquidity. Now it's not so black and white and it doesn't always have to be a "full-time income." It depends what their goals are. E.g., 1) At Airbnb, renters aren't looking to quit their day jobs and become landlords full-time... they're just look to earn a substantial amount of income to offset their rent, mortgage, etc. So in this case, I would probably goal on # of renters that earn >$500 / month... and (in the first 1-5 years) try to grow this number by 10-20% MoM... and maybe by just 5% once you're in the mid-high tens of millions in yearly revenue. 2) At Kickstarter, the goal of the supply-side is to get their project successfully funded. They don't care if the project creator is "full-time"... they just want to make sure they meet their funding goal. This is why they talk about their 44% project success rate all the time - http://www.kickstarter.com/help/stats 3) At Udemy, our instructors want a substantial amount of their income to be driven from their Udemy course earnings... so we look at how many instructors are earning >$2k / month.