Older trade paperbacks usually have glued bindings... The signatures are basically glued to the cover...and that's it.
Over time some glues will dry out and the binding will crack...leaving loose pages or even a total seperation of the cover from the pages.....
Often a book will look fine...to the bookseller....but once the buyers tries to open the book and read it...the pages quickly loosen...and you get an angry or concerned email about the bad book you sold them...
Perhaps booksellers should test these old bindings not just for their cosmetic appearance at the time of shipping...but also for their ability to function... when the book is actually used and read?
I will often place a cloth tape re-enforcement between the FFEP and the cover if it looks like the cover is about to seperate....
Or if it has already seperated...I always re-glue...and that is an even better solution.... Apply the glue...stabilize the book... and let dry over night.... Should be "like new" in the morning...perhaps even a bit "too tight."
Unfortunately some books look OK to send...and you hate to "alter" the appearance with tape ....so you take a chance that the buyer will assume responsibiity for any "future" damage....
Well some do...and some don't.
Older trade paperbacks need special examination for these dried out bindings...just to be safe.