Negotiation 101 with Professor Gagosian

From David Segal's piece on art dealer Larry Gagosian in The New York Times:
Harvey S. Shipley Miller [trying to buy a Cy Twombly drawing for a non-profit foundation that would donate it to the Museum of Modern Art—other dealers had offered a discount]: “So I said, ‘How about $100,000 off?’”
No, Mr. Gagosian replied.
“How about $25,000 off?”
“Nope, I can’t do it.”
“O.K., Larry,” Mr. Miller said, exasperated. “How about $1? Can you give us a dollar off?”
Well, no.
“I tell you what, though,” Mr. Gagosian answered. “I’ll buy you lunch.”