Personally, I don’t consider books dropped off at shows as “hand” delivered. I drop off books at their facility, and even with that the books get moved around more than one would think.
Additionally, regarding poly-bagged books there is an expectation that because they have been bagged the book must be near mint or better in condition. Personal experience has proven to me the exact opposite is true. If they were poly-bagged and boarded I could see thinking this way, but the poly-bag is little more than a Saran Wrap and the book can, and usually does get damaged by rough handling or by the bag itself.