What key risk factor is associated with customer concentration in potential investment opportunities?

The key risk factor associated with customer concentration in potential investment opportunities is when a single customer accounts for more than 5-10% of total revenue. This level of concentration presents a red flag for investors because it indicates reliance on a limited number of customers for a significant portion of revenue. If the company were to lose that customer or if the customer were to reduce their orders, it could have a detrimental effect on the company's financial health.

High customer concentration can lead to volatility in revenues and a lack of diversification, making the business more susceptible to market changes and customer-specific problems. Therefore, monitoring the percentage of revenue generated from large customers is crucial for assessing the stability and risk profile of a business.

The other choices highlight different aspects of customer relationships and contracts but do not specifically address the inherent risk tied to revenue dependence on a small number of customers, which ultimately affects the investment's risk assessment.