Disputed Banksy Work in Miami: What About That Estimate?

If you haven’t seen the stories about a Banksy wall work that mysteriously disappeared from the side of a London store only to reappear in A Miami auction catalogue, you can get the gist here and see the auction catalogue here.

But what is doubly curious about this sale is the estimate of $500-700,000 on the work. Where does that number come from?

Update: As Shane Ferro points out there was a recent sale for $614k at Sotheby’s, the highest price achieved since the crash.