What factor could most likely indicate the existence of related parties?

The presence of borrowing money below the market interest rate is a significant indicator of related party transactions. Such transactions often occur between entities that have a close relationship, where typical market conditions may not apply. For instance, companies may provide favorable lending terms to related parties as a way to support a family member’s business or an affiliate. These preferential terms can manifest as loans with reduced interest rates, which would not typically happen in an arm's length transaction where both parties are independent and striving to maximize their own financial outcomes.

In cases of related party relationships, transactions might not reflect true market conditions and can sometimes lead to financial misstatements if not disclosed adequately in the financial statements. Thus, the presence of below-market interest rates strongly suggests that the lending is likely between two related parties, differentiating such transactions from standard business activities.

The other options might indicate various business issues but do not specifically point towards the existence of related parties in the same way that below-market borrowing does.