This is something which is really a challenge.
In many markets discovery is a challenge (how do you create visibility to all of the customers who might be interested in your product) and then operational costs when your concept is discovered.
When brainstorming things I heard an idea which I thought was pretty cool, create a "trademark" registry in these bespoke market places. It would work by sending the market maker (Etsy in this case) pictures and a description of an item you are going to sell on the site.
They would take those images and descriptions and first verify that nothing else on the site already had both the same look and application, and then they would issue you a "trademark" for the product which you could start selling and advertising. If it was popular and someone tried to make copies, they would not be allowed to sell them on Etsy because when they submitted pictures and descriptions it would be apparent they were too similar to an existing product.
It is interesting to consider what the overall effect of such a system would be, we know that it would give a strong 'first mover' advantage (+1 to the sellers) but also prevent price competition (-1 to the buyers). It would help prevent counterfeits (+1 to the buyers) and might limit a seller selling their own product because the copy had already gotten to the market first (-1 to sellers).
I put trademark in quotes because while this is exactly the role of trademarks in the US, it is too expensive to pursue trademark violations for a $10 bracelet that you sell may 20 a month of. So you need a locally implemented system that can reduce the cost to implement and as much as possible automate enforcement through policy.