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

Freemium revenue for mobile apps was up 211 percent last year (2013), according to a report from mobile analytics company App Annie and IDC. 83 percent of the top thousand apps on each of the iOS app store and Google Play — monetize via freemium, an even bigger proportion of revenue generated by those top 2,000 apps arrives via freemium: 92 percent. Naturally, the key to success as an app developer who uses the freemium model is getting as large a percentage of your free users buying something as possible. That’s a significant challenge. You have to do what makes the most sense for your app and the users on it. You must create value for the user and make it compelling for them to spend money on whatever you plan on offering. In terms of viable it is tough to say because I don't know what your medical app does. 1. Look at the data from your app 2. Talk to your users about what they want 3. Look at what your competition is doing or others in a similar vertical

Your support software should cater to your needs, depending on how your business operates. Fiver uses Vanilla forum and Zendesk. Thumbtack uses Zendesk. Not sure about AirBNB, their help center seems to be custom. Depending on how well funded your are, I would recommend starting with a free plan with one of the help desk SaaS products, or even using open source ticketing platform. Then, as your needs grow and you need integration with your marketplace, there's no reason you can't scale and migrate.

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.

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.

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.