Ask HN: Defeating the marketplace problem?

Hi guys,

A lot of my best ideas tend to fall into the "marketplace" category and therefore hit the main problem of marketplaces. That is, buyers have no interest in using the marketplace with no sellers, and sellers won't benefit from listing on the marketplace without active buyers.

There must be a good way to defeat this problem? The best I have come up with so far is really pushing one side (probably sellers) to join with various incentives and so on, then once there are a decent amount of sellers, go crazy driving traffic to bring in the buyers. This seems like a "naive" approach though.

Another option is to seed one side yourself (like Reddit did, or most new forums) creating new seller profiles with things to sell and manage it all yourself. Quite a challenge.

What are peoples thoughts on this? Surely there must be plenty of people on HN who have run into this problem with their own projects. What did you do to solve it?

Thanks!