Like Dave, I'm rather confused whether you're making a statement or asking a question; if the latter, what's the question you're asking?
However: Auditor is the simple singular: "She is an auditor". Auditor's is the possessive singular: "It is an auditor's desk". Auditors is the simple plural: "They are both auditors". Auditors' is the possessive plural: "The auditors' office is in here".