The trick only works because the book is considered published yet it is out of stock so has to be back ordered.
And these back orders still count for the NYT bestseller list.
My guess is they somehow triggered some sort of last second revision for their own book at the publisher thus pausing the printing.
So the book is technically published and available in various catalogs yet you can't actually buy it. You can only back-order it.
I assume if you could actually order the book the "buyer" would have to shell out some cash.
An additional trick is that the "buyer" is being careful not to trigger bulk buying clause for each store.
It is basically the click farm equivalent online.