I feel like if the seller posts a book for sale, with no back scan, but states in his opening that pictures are available if you want to see them he is honest. If it is a low dollar book, most are, I am agreeable to this route. If it is a 750$ book like mentioned above, I agree there should be BC scans/pics. Same goes for slabs, although, if the seller lists the graders notes that should suffice or if he states any glaring BC defects in the write up since the grade is made clear by the slab. Finally, if it is someone that I have bought from before and feel comfortable with, then I am fine with. I suppose, the other thing that comes into play is the return policy. If there is no BC scans and no return policy, I'm out.