The Amazon UK Daily Deal for Sunday 12 May 2013 is the first four "Lovejoy" books by Jonathan Gash.
First book's blurb:
"Every antique dealer is a bit of a detective, following clues to find the trophies that pay the rent, but when Lovejoy takes on the job of tracking down a pair of duelling pistols so rare that he's not even sure actually exist, he needs all the instincts of a detective to pick his way through an unsolved crime."
UK Daily Deal