Why did the star lot of the spring season, a bronze head by the master sculptor Alberto Giacometti, fail to sell at Sotheby’s? Alberto Giacometti’s 1955 bust, “Grande tête mince" (“Big Thin Head”), carried a pre-sale estimate of $70 million in Sotheby’s Modern evening auction. The auctioneer started the bidding at $59 million dollars. But no one bid - the piece went unsold. It was the second high-profile lot to disappoint in two days. Andy Warhol’s “Big Electric Chair” (1967-68) was withdrawn from Christie’s 20th century evening auction the day before. Is the fine art market in trouble?