I heard the following story from Haj Ross, a friend and teacher. I don’t know it’s origin…it might be a fake.
Picasso is painting in his studio, when an art dealer comes to see him.
The dealer says, “Monsieur Picasso, I have just bought this painting, which was said to be a genuine original. But just to be sure, and in order not to perpetrate any fraud, I have brought to you for authentication.”
Picasso casts a brief glance at it and says, “It’s a fake.”
This is a great loss for the dealer, for he is an honest man. But he carries on, and in four months, he returns with another painting.
Picasso glances at it too, and then says, “It’s also a fake.”
“But cher maître!” expostulates the dealer. “When I visited you last summer at your atelier in Cape d’Antibes, I saw you working on this very canvas. How can you now tell me that it is fake?’
Picasso shrugs. “I often paint fakes.”