Sublist on Partner record that shows Sales Rep of its Customer relationship

A. Create saved search.
1. Navigate to Lists > Search > Saved Searches > New.
2. Click Customer.
3. Enter Search Title.
4. Click on Results tab.
5. Add or remove fields as needed. (Make sure to include Sales Rep)
6. Click on Available Filters tab.
7. Select Internal ID under the Filter column.
8. Mark the Available as Sublist View checkbox.
9. Click Save.

B. Create Sublist.
1. Navigate to Customization > Forms > Sublists.
2. Under the Search column of the Entity tab select the saved search.
3. Enter a Label. (Ex. Other Relationship Sales Rep)
4. Select a tab under the Tab column. (Relationships)
5. Mark the Partner checkbox.
6. Click Save.