Very tough to tell without the book in hand, and even then...
The right hand margin isn't straight (hold a piece of paper up to your monitor to verify), but the cover follows that same, very gradual curve or crook (lumber term). A book can certainly move slightly while it's being cut at the printer. In those two preceding pics, it looks like there is more of the back cover showing at the bottom than the top, so you should see less of the front cover at the bottom, all other things being equal. In fact, there appears to be a bit more front cover on top. This could however be explained that the cover is pulled away from the staples and the rest of the book more so at the top than the bottom. From the pictures, this may be the case.
The corners do look very sharp, but perhaps the front cover was better protected because less of it was exposed beyond the page edges.
Of course it's a frustrating exercise when you can play devil's advocate like this - raising issues, and subsequently explaining them away. I would proceed cautiously and share your concerns with the seller.