A geezer sees a sign in front of a house: "Talking Dog for Sale." He rings the bell and the owner tells him the dog is in the back garden.
The bloke goes to the backyard where he finds the black mutt just sitting there. "You talk?" he asks.
"Sure do." the dog replies.
"So, what's your story?"
The dog looks up and says, "Well, I discovered my gift of talking as a young pup and I wanted to help the government, so I told MI5 about my gift, and in no time they had me jetting from country to country, sitting in rooms with spies and world leaders, because no one figured a dog would be eavesdropping. I was one of their most valuable spies eight years running. The jetting around really tired me out, and I knew I wasn't getting any younger and I wanted to settle down. So I signed up for a job at the airport to do some undercover security work, mostly wandering near suspicious characters and listening in."
"I uncovered some incredible dealings there and was awarded loads of medals. Had a wife, a few puppies, and now I'm just retired."
The geezer is amazed. He goes back in and asks the owner what he wants for the dog.
The owner says, "Ten quid."
The bloke says, "This dog is amazing. Why on earth are you selling him so cheap?"
"Cause he's a f@cking liar. He's never done any of that stuff ..."