Edited excerpt (some rewriting, reduced list) from 14 Marketplace Mistakes That Are Killing Your Startup by Tristan Pollock:
1. Poor risk management. Ensure you win the trust of your customers, and watch out for their safety.
2. Smart risk management without self-promotion. Let your customers know about your marketplace protections early in the dialog.
3. Not building a movement. Capture brand equity for your company early on.
4. Not regulating your community. Moderate and curate a lot, especially early on in the life of your company.
5. Over regulating your community. The more you relinquish control to the community, the better the experience, the more engaged the community, and the faster you can scale.
6. Focusing too broadly.
7. Over optimizing on price (setting your rev share too high).
8. Getting the balance wrong between quantity and quality.
10. Preventing disintermediation instead of adding value.
11. Over catering to supply customers. Sellers are the most vocal. Buyers are silent judges of your success: treat them well and they’ll spend money, otherwise they’ll just silently disappear.
12. Thinking marketplaces are easy exits. Marketplaces take much longer to reach product-market fit, liquidity, scale, and are often a 5-10 year venture before you’ve nailed it.
(1) Thank you Asi Segal for the tip.