Large software vendors usually have clauses in their contracts that allow them to audit your installation - and in some cases tie this audit to revenue reportin

Large software vendors usually have clauses in their contracts that allow them to audit your installation - and in some cases tie this audit to revenue reporting. If you're a public company this is all easily auditable, but even a private company can produce an accounting report. There's usually some level of trust involved unless there's reason to suspect you're "cooking the books" for your report.