When dealing with duplicate leads, even if a standard Matching Rule is in place, it may not be sufficient if specific custom criteria are needed for identifying duplicates. In Salesforce, it's possible to create custom Matching Rules that use criteria tailored to the business's unique data requirements. Activating a custom Lead Matching Rule ensures that leads are matched based on those specific attributes, which can be more effective at identifying duplicates than the standard rule alone. The consultant should verify that the custom rule is active so it can be used to enforce lead uniqueness.
For details on Matching Rules, see Salesforce's documentation on Setting Up Matching Rules.