I think he means 30-60% of the items listed sell, not 30-60% of the visitors sign up. Not sure how you count this when you expect repeated transactions - perhaps for AirBnb it means properties are booked 30-60% of the time. Liquidity is also about the sellers at the marketplace, not it's owners successfully exiting.
I found the point about (de)centralization of different aspects of the marketplace interesting, can you point me to more advanced resources about marketplaces?
I found the point about (de)centralization of different aspects of the marketplace interesting, can you point me to more advanced resources about marketplaces?