Perform checks however often it takes to accurately represent to Wizards, when asked, that no person you engage has been convicted of any offense listed in the WPN Terms and Conditions.
A background check is sufficient if allows you to accurately represent to Wizards that the subject of the check has not been convicted of any offense listed in the WPN Terms, under any applicable law.
There are many agencies and services that can perform such a check. We recommend that you use a reputable third-party reporting service.