How often should a trading business do an in-dept investigation into the financial competencies of its vendors and other creditors?

Financial competencies of vendors may be assessed vis-a'-vis their abiity to ensure uninterrupted supplies to a trading business.

Moreover, vendors' demand for advance payment or payment earlier than the due date; may signal doubts of their financial competencies.

Once a year would suffice once a due dilligence is done before signing up with them at Stage 1. However the financial compentency of a debtor is much more important than a creditor.