File this under ideas we’re open to but not sure about. This Saturday (March 24) is National Cash Mob day, which is designed to get people to spend money at local businesses. Amy Cortese, the Brooklyn-based author of Locavesting, is spearheading Brooklyn’s first on-the-spot shopping spree at an as yet undisclosed Park Slope business. To join in, show up at Tea Lounge at 4 p.m. on Saturday with $20 in your pocket to spend at mystery shop, plus a few more if you want to go drinking with the crew afterwards. Our friends at Brooklyn Based have the whole story here.