If you'll give a sneak peek with your design which can be more attractive with other builders, you might the attention from the people who are longing to create their own website/marketplace.
If you could make users make their own pages in your site, that would be better, It's also free advertisement for you.
Just like almost the same what's on my mind, allowing users to use your service for free with a certain period of time or something like what OmegaStarScream.
How do you think where we can find people who want to make site to sell their goods and services for bitcoins?
Try to look in Services.