L: Ca-D'Oro (1964) R: Spike (1964) both by John Chamberlain
Photo: Sotheby's, Christie's Images Ltd via The New York Times

Take a look at these two 1964 sculptures by John Chamberlain. The one to the left, titled Ca-D'Oro is valued at between $1.8 million to 2.2 million by Sotheby's whereas the one to the right, titled Spike, is valued by Christie's at between $900,000 to $1.2 million.

They look the same, made by the same artist in the same year. So why the price difference? Carol Vogel wrote an article for The New York Times about the pricey world of art:

Both of these colorful crushed metal sculptures are from the artist’s prime period, when he used everyday objects, like abandoned car parts. He often sprayed as many as 100 coats of lacquer on the steel to achieve the surface he desired.

Estate property is generally more reasonably priced, and Christie’s has given the Lawrence heirs a guarantee. That means the auction house rather than the estate can set the prices. The one at Sotheby’s seems to have been estimated at the whim of an auction house expert — or possibly a hungry seller.

Link - via Book of Joe

Better question: why is it worth so dang much in the first place?