The pricing benchmark for art is traditionally set through auction sales. However, this metric could become unreliable in determining the art market size. Global auction house sales have declined 18.8% year on year to $16.9bn. Private sales by dealers have increased as much as 25% annually, accounting for an estimated 70% of all sales worldwide. The latest art market report issued by the European Fine Art Foundation suggests buyers and sellers are increasingly seeking privacy and opacity, away from transparent auction dealings.

Gallery sale figures occasionally emerge, particularly when markets do well, which was the case at the 48th edition of Art Basel in May. On the first VIP preview day, it was reported some dealers had concluded sales in the tens and twenties of millions of dollars. By the second day, against a climate of economic confidence, it was announced the David Zwirner gallery had achieved more than $40m in sales. Highlights included Italian artist Alberto Burri’s Sacco (1954), which sold for $10m and a selection of paintings and works on paper by South African-born Marlene Dumas priced between $150,000 and $3m. read more