Nobody is buying S9's at $400. ...nor are the newest S9's going to sell out....there are 10's of thousands of them for sale through Offordscott alone.
S9's will be obsolete SOON...by Oct. most will be mining at a loss,  because of the Diff increase from new gear and the price WILL DIVE again as new gear comes online worst dive will be before year end. Diff will double by year end to 20 Trillion.