You might want to stop in at the Whodunit? bookstore. It's at 1931 Chestnut Street, Philadelphia, PA 19103. Inside in tight, somewhat haphazard-looking shelves, you'll find an assortment of mostly used books, mostly paperback. I'd say mostly mystery or crime fiction—they were specialists when they started—but now I'd say half-and-half, half mystery, half general interest.
The great strength of stores like this is they have a broad selection for the aficionado of hard-to-find, out-of-print, and even rare books. Let's face it, no matter what my tastes are, the world of popular books is more aligned to Fifty Shades of Harry Potter than to David Goodis. (I bought his classic, Black Friday.) Or more comfortable with werewolves, vampire hunters, ghost walkers, and horse whisperers than with Seven Slayers (I also picked up the Paul Cain collection by that name.)
A weakness is that at any given time, stock is more hit and miss than Amazon. For example, I'm looking for The Chill by Ross MacDonald, but I settled for The Far Side of the Dollar, the most interesting-looking Ross MacD. on the shelves. (I suppose a wag might argue all Ross MacDonald novels are the same anyhow.)
Another nice thing about this store is that you might meet one of the principals and share a few minutes of conversation about a common interest. I met Henry Reifsnyder, as nice a fellow as you're liable to run into in Philly, and we talked a little about P.I. novels, and mid-century American noir. Henry was great, steered me to a couple titles I might have overlooked, and gave me a tip on an agent.