Create a Saved Search that Shows Entities of Type Set to Both Contact and Customer (Other Relationships)

1. Navigate to Lists > Search > Saved Searches > New.
2. Choose Contact.
3. Provide a Search Title.
4. In the Criteria > Standard tab, add Formula (Text).
5. Set Formula: CASE WHEN {internalid} = {customer.internalid} THEN 1 ELSE 0 END
6. Set Formula (Text) = is 1
7. In the Results tab, set fields as necessary.
8. Save.