Possible Clues:

• Buyer and seller of oils
• Theo van Gogh, notably
• Gallery owner
• One making money with other people's work?
• Read later about sale of oils by this trader
• Free trader is stocking Goya, Chagall and Cezanne at last
• Theo van Gogh's occupation
• One concerned with oil prices?
• Forger's mark?
• Iceberg's cousin