The Practical Guide to building an online marketplace is written by Christóbal Gracia and Juho Makkonen. All articles are available in Marketplace Academy and as a book, Lean Marketplace.Article available at:
How to validate your marketplace idea before building the platform, Christóbal GraciaSources and further reading:

What can be learned when sharing leads to failing, Pando 

Spotify: the unproject culture, Henrik Kniberg 

The only thing that matters, Pmarca Guide to Startups 
Video: Validating Product/Market Fit, Steve Blank 

How to build a Minimum Viable Platform, Marketplace Academy 

Platform Design Toolkit, Boundaryless 

Simone Cicero: How to design your marketplace idea, Marketplace Academy 

The Lean Startup, Eric Ries 

Running Lean, Ash Maurya 

The Startup Bluebook: The Entrepreneur’s Guide to Customer Development, Brant Cooper 
Video: How to Use the Validation Board to Test Your Startup Idea, Lean Startup Machine 

All Markets Are Not Created Equal: 10 Factors To Consider When Evaluating Digital Marketplaces, Bill Gurley 
Video: How to Validate Your Marketplace Webinar, platformOS 
Video: The Lean Approach: The Lean Method, Kauffman FoundersSchool. 

The Business Model Canvas, Strategyzer
Two-sided – The marketplace podcast: Talk to your users before building anything with Charles Armitage (Florence), Sharetribe
The Marketplace Academy Podcast is hosted and narrated by Katri Antikainen.Learn more about building a marketplace at www.sharetribe.com/academy/.Looking to build a marketplace of your own? Visit www.sharetribe.com!