If I had one piece of advice for someone trying to build a new marketplace, stop trying so hard to be a great marketplace first.  But what to do instead?

Try hard to be a great retailer.  What do retailers need to be great at?

• Identifying new up and coming brands.

• Marketing these brands existence to the world.

• Communicate the essence of your great new found brands to your buyers.  Engage their emotions.

• Acquiring new consumers.

• Setting proper consumer expectations.

• Knowing your competition and your customer's alternatives, and finally.

• Keep raising the bar on your experience.  The sun never sets on your consumers' #ecommerce expectations."

Then, layer in the marketplace parts on top of that.  Many people are too busy trying to get their marketplace flywheel going that they forget completely why retail consumers are there in the first place.