They also completely bypass the chicken/egg problem. The site can work with a small number of sellers. If I'm an artist I can set up a store on etsy and use it

They also completely bypass the chicken/egg problem. The site can work with a small number of sellers. If I'm an artist I can set up a store on etsy and use it as my professional website. I then give out the etsy link to people I meet in the "real world" to buy my work online.