The last several years I've worked for companies using Concur and Expensify. None of the employers have had special auditing done by the services, just basic compliance checks like "Flag if a receipt is not included" and "Flag if meal expense is over guideline." Any questioning of an expense, or rejection of an item/report, comes from someone within the employer. It wouldn't surprise me if the expense services offered greater auditing capabilities; though if so none of my employers have utilized them.