I assume you're referring to building out a store with no inventory to test the market? This is a pretty common tactic spread by books such as "The 4-Hour Work Week" so it's not surprising to see it in use for a site like this.

Honestly, I don't really have a problem with it. A more honest approach would be ideal, but if I had to choose between doing that and bootstrapping an entire business with stock before getting my first sale I would choose the "dishonest" method. It's a little inconvenient for the user, but presumably they want the product, so in the end they just end up waiting a bit for it.

People don't want to help you test your idea, so presenting it in any other way without rewarding them is unlikely to result in sales.