The clamor over potentially inflated appraisals in a cooling housing market may have reached a fever pitch in the past six months, but the specter of tainted loans has not undercut the quality of mortgage-backed securities. Bad appraisals are always a concern, but especially so in areas where home prices have risen rapidly and you can see some degree of appraiser bias toward higher valuations, said Fitch analyst Glenn Costello. But the rating service…