This week, around 60,000 of the world’s well-heeled will visit the annual Frieze Art Fair, in London’s Regent’s Park, and its satellite shows. Some visitors will be big collectors like Roman Abramovich and celebrities Brad Pitt, Gwyneth Paltrow and Karl Lagerfeld. While buyers are expected to spend millions at the shows, many galleries are suffering from diminished prices and inventory. Data provider ArtTactic says prices have fallen by as much as 40% in the past 12 months.