In my experience there are only a few cities in the U.S that literate people are proud enough to live in, that they would be insulted that you put that into your crap town book.
Thus I wonder what demographic that at one time would have bought this book is not going to be buying this book now.
Considering the book is about "crap towns" in the UK, I imagine it could be a very different demographic than the one you're thinking of
hmm, maybe. In the U.S you have often the person who moved from a 'crap' town to some place they consider great, who gets really emotional about the crappiness they escaped to be able to think freely and the like. And often these people are the ones I would think of as customers for a book like this, and if their new town isn't in the book they certainly won't be offended.
A good way to identify which cities suck is to say to a native "<their city> sucks".
If they agree that it sucks, it probably sucks.
If they get really mad and defensive about it, it definitely sucks.
If they're just bemused or laugh it off, it's probably nice.
The funniest thing about that is that the cities where these proudly smug people live have the most actual crap on their streets.