JEWELER'S ADVISORY GROUP FIGHTS AGAINST DECEPTION The industry's newest watchdog organization is about to mark its first full year of quietly but aggressively providing support for jewelers and consumers stung by deceptive practices. The non-profit Jeweler's Advisory Group was born &endash; almost unexpectedly &endash; Jan. 1. A few days earlier, Jay Mendenhall, a retailer in Beaverton, Ore., put a note on the Polygon computer network asking jewelers interested in stopping deception to respond. Within a few hours, he had so many responses that he spent the next few days compiling a 13-page portfolio outlining how they could band together to fight deception in their cities or their regions. "People reviewed the portfolios and started to ask what they could do to help," says Mendenhall, a 25-year industry veteran who studied jewelry design and gemology in Thailand and now spe