Search Customer Records with Only One Opportunity Associated to them

1. Navigate to Lists > Search > Saved Searches > New.
2. Select Customer.
3. Navigate to Criteria tab > Standard subtab > Add Opportunity Fields: Date Created is within today:
4. Criteria tab > Summary subtab > Summary Type = Count > Field = Formula (Numeric) > Description = is 1 > Formula = {opportunity.internalid}
5. Click Save & Run.