On the perils of looking at a title page

Last week, I showed my intro to grad studies students one of the perils and pleasures of working with nineteenth-century (and earlier) books: the presence of multiple texts in what appears to be a one-work volume.  (Entire books have been "lost" and "found" because they were bound in with something totally unrelated--a fact nowhere heralded on the title page or binding.)  Bookdealers don't always look beyond the title page, either, which is why I just discovered that the set of two tracts I thought I was purchasing turned out to be the full run of twenty-six.  Not that I'm complaining, mind you, but the eBay seller would have got rather more than $10 USD if bidders had known that s/he was offering a quite rare complete set!