What was found
AIRCRAFT WAS GNDED. DURING TAXI OUT FLIGHT ATTENDANTS REPORTED AFT & MID CABIN FUMES, SOCK OR SHOE POLISH TYPE SMELL. THE ACFT RETURNED TO GATE & THE ACFT WAS TAKEN OUT OF SERVICE. ACCOMPLISHED JC 26L00021001, TROUBLE SHOT CABIN AIR QUALITY. NO ODOR NOTED. CAPTAIN DOCUMENTED ON THE ACFT CABIN ODOR REPORT FORM 8533, BELIEVED THE CAUSE WAS EXTERNAL AIR CART, TRUCK DOING ENG START, ACFT WAS RETURNED TO SERVICE.