Accustomed to generous retail return policies, jewelry store shoppers aren’t afraid to bring merchandise back. Here’s how to craft a friendly return policy without sacrificing your bottom line.   When the issue of returns comes up, David Audette, co-owner of M.R.T. Jewelers in East Providence, R.I., sighs deeply. For years, M.R.T. held a forgiving return policy, one that ­honored multiple generations of customers at the century-old store. “We’d even take back custom-built pieces if we felt we could use certain components again,” Audette says. “There was no way we could’ve been more liberal than we were.” Now, however, Audette is rewriting M.R.T.’s return ­policy, carefully crafting guidelines to better insulate the business from losses. “The goodwill we’ve extended to customers hasn’t ­necessarily been returned,” Audette explains. “Jewelers need to