Carmaker Henry Ford supposedly said that half the money he spent on advertising was wasted; he just didn't know which half. Mark Perez and Sebastian Igreti, co-founders of TechMD, a Costa Mesa information technology service, can relate to that sentiment. "We're tech experts, but we don't know how to market," Perez said recently. "We've done six different types of marketing: postcards, letters, prize drawings, online, cold calling. Nothing worked." Until now. In 2011, TechMD wanted to support one of its clients, the Girl Scout Council of Greater Los Angeles, so TechMD bought 2,500 boxes of Thin Mints to send …...