Who's running a marketplace? How did you tackle the chicken/egg problem?

We just built Terrain (https://knowtheterrain.io), it's definitely a challenge, but we used personal networks to secure the supply side first, and are working on cracking the demand now

I am building a marketplace now, and focused on the supply side first. Think about what side needs the other side more (for me this was the demand side) and then focus on building that side more (for me the supply side). I hope this helps - and check out what we are doing at Barter (https://coral750.softr.io/)!

This might be helpful - https://www.lennyrachitsky.com/p/how-to-kickstart-and-scale-a-marketplace

I don't run one anymore, however when I did the key was to start within a niche and specific geographical area – Also there was an existing community and content, so I already in a way had the demand.

For example if I had a Cycling page for people within the Manchester area, it was easy to add in a Buy/Sell to that Blog, which would naturally get traction – Over time you can then expand the geographical area, and also expand out of the Niche.