How important is it for a marketplace startup to drive enough demand (customers) for your supply (sellers) to make a full time living off of it?

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.

Need more info in your question. Is it so that you the marketplace owner can make a living, or the suppliers?

Obviously the value of a marketplace is liquidity for both demand and supply. However, suppliers are more likely to bear the cost of "waiting" for demand, since they are the ones trying to make a buck (and because "those with the gold make the rules").

If you can build your marketplace in such a way that sellers are able to embrace it without immediate gratification (e.g. no opportunity cost to the seller), then you can build up supply to then take to the demand side.

It's a tough balancing act, kind of like "walking" a big piece of furniture across the room.

The answer depends on several factors, but much comes down to what alternatives they have. If it's costless for sellers to join your platform, and they are able to join competing platforms (multihoming, in the lingo of two-sided marketplaces) or earn money in other ways, then there's no need for them to make a full-time living off selling on your platform. On some classic platforms--including eBay--many sellers are happy to participate as a sideline.

It is important especially start-up drive enough demand. Let us look at it in details:
1. “On Demand Services caters to the vast spectrum of user’s need.”
Services ranging from medical services to business consultancy are also utilized with the help of mobile applications. It has also led to the increasing demand for mobile app developers that resulted in a rapid increment in the number of mobile apps development companies. As observed, everyone who gets exposed to advanced technologies like a smartphone is aware of how things work on smartphones and how it is possible to book various services through a mobile application. As a result, web portal dependent customers have shifted their dependency to mobile applications, and this has mushroomed the start-ups offering on-demand services such as Uber for transportation services, has effectively leveraged on the taxi app development. While on the other hand there is Groffers for groceries, and HourlyNerd for business consultancy services to name a few.
The Uber for X model is also a collection of different types of on-demand services that aim to save time. The on-demand economy is growing continuously at a rapid rate considering the growth rate of start-ups like Uber, Ola, Jugnoo, Zopper, and Urban Clap. Uber has managed to raise approximately $10.2 billion, Urban Clap has raised nearly $35 million, and Ola Cabs has raised nearly $1.18 billion after having completed seven stages of funding. Surely, on-demand start-ups have turned out to be more convenient, more technically updated, and highly efficient. However, there have been various reasons for people to start relishing on business ideas like Uber as they are more user-friendly and easier to use. Accuracy, speed, quality, and customer satisfaction are the values that shape up the on-demand economy. It has motivated youngsters for implementing their innovative ideas and managing to retain their start-ups in an efficient way. By carefully observing the prevalent factual advantages, it is quite evident that this trend of utilizing services has turned out to be a success for investors, customers, and start-up owners. However, more reasons have attracted the concerned authorities and business entrepreneurs towards the on-demand economy.
2. “Investors have also started considering these on demand start-ups as a big source of attraction as they have the ability to predict the future of each and every trend that results from technological and business integration.”
Customers’ expectations have been increased due to such high-quality services that are being offered in a short time span. Due to the high availability of options, customers either prefer to get the desired satisfaction level, or they tend to look for other options. It has made the on-demand economy more competitive for the businesses. On the other hand, the increasing demand is used as an opportunity for investors and industry tycoons to shift their focus to on-demand business. The credit for the success of on-demand mobile apps goes to the customers who have learned to take an advantage of the smartphones. It has shaped up a new apparent world where any service can is easy to book with just a few clicks. The pioneers in the concerned area, industry tycoons, and investment agencies that keep their eyes over an on-demand economy at a bigger level believe that the world is witnessing the first phase of a rapid shift to the on-demand business. The hidden yet vast potential within the various departments is unfastened by many entrepreneurs. Customers or end users have also managed to reciprocate appropriately by appreciating the advantages of the on-demand business.
3. “The scope of On-Demand business is bound to scatter to various industries in near future.”
The entire model of on-demand start-ups seems to be a highly efficient model and a big success shortly. After having observed the way it has changed consumer behavioural patterns and buying patterns, it would not be an exaggeration to claim that the on-demand economy might lead to more and more start-ups catering the needs by offering essential services like water, delivering gas cylinders, and repairing the damaged electronic equipment. The primary focus is on how on-demand mobile applications can decrease the efforts of consumers without compromising the quality of services. Several on-demand start-ups and businesses have made it easier for customers to have access to solutions by offering a symbiotic equilibrium for the ongoing on-demand economy. However, the four values that would grow the already growing economy at a faster rate are speed, accuracy, convenience, and quality. It will be made feasible by the genuine efforts of mobile app development companies that, at times, do not manage to retain the user-friendly nature of mobile applications and to provide customers with a highly satisfying experience due to management issues.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath