What to do if one buys silver pieces and finds idolatry among them: Bechorot 13b
Concern for suspicion of possessing idolatry if one purchases silver pieces with money and then discovers idolatry among them, so that when returning them the Jew receives money back and appears to be selling idolatry: Bechorot 13b
Benefitting from items which were exchanged for idolatry: Kiddushin 17b