Every art buyer has a financial interest in increasing the value of the art they've bought. One reason that Christies can charge substantial fees is that it se

Every art buyer has a financial interest in increasing the value of the art they've bought. One reason that Christies can charge substantial fees is that it serves as a guarantee that the transaction is somewhat real. If an artwork changed hands privately between friends for $1M, there'd be no reason to believe that price. But when they're paying a 15%+ fee to an auction house, there must be something valuable.