It is more of a case of that "5.5" actually needing to be labelled properly as a 4.0/4.5 with that big of a piece missing. The price was fine if you look at it that way. I disagree with the way CGC is so lenient with pieces missing. I have a Strange Adventures #205 up on eBay that I was grading as VG with no takers as a raw book at local shows due to the missing pieces/chips. It came back as a 6.0 in a nice slab.
Add in the apparent edge tear in the middle of the right side, what appears to be a color breaking crease in the bottom right corner, and a longer crease or tear (or scuff?) at the bottom staple and I am surprised this came back so high.
FWIW, Clink limits the prices on all books by not providing a back cover scan. It looks like there is a bit of a bend/crease in the tip of the top left corner of the back cover on this B&B #28 (slabbing issue?). If I am spending a few grand on a book I would like to be able to see both covers. That is not too much to ask, is it?