Sounds like great fodder for a Python sketch.
BOOK SHOPKEEPER (CLEESE): That's 5 pounds, please.
CUSTOMER (PALIN): For what?
S: You were looking. At our books.
C: Yes. That's what people do in book stores.
S: Maybe in other establishments, but not here. You want to browse, you pay for the privilege.
C: That's ridiculous!
S: Oop! Now you're glancing at the cover of 50 Shades of Grey
. That's another 5 pounds.
C: I wasn't looking at it.
S: Yes you were.
C: Prove it!
S: It's right here on the photon collector.
C: What photon collector?
S: This big box right here. Found it in the dumpster behind the CERN laboratory. It measures the number of photons that hit various objects and tells where they came from. It says here that six of yours landed on the cover of this copy of E.L. James' classic, fanfiction-cum-erotic fiction masterpiece.
C: I'm not paying you ten pounds to browse a few books!
S: Tell you what--make it three pounds and I'll give you the glances at the two books you looked at already plus a 30-second thumb-through of this month's Jugs and Bums
C: (thinking) Is it the one with the Pippa centerfold?
C: Two pounds six.
(And so on).