Five pieces by the mysterious British graffiti artist Banksy went unsold at an auction of street art in London over the weekend, mainly owing to the artist's authentication agency's refusal to endorse the five stencil and spray-paint works on the block, which had been removed from their original contexts. This failure to sell is raising serious questions about the health of the art market in light of recent economic turmoil, and confidence in the future of Banksy's marketability: In a time when even the wealthiest patrons have to watch their wallets, dropping a huge sum of money on an unendorsed (and easily faked!) work by a famously elusive artist is not exactly the safest bet. [Bloomberg]