Power Pivot & duplicate values

I recently changed to a version of Excel with Power Pivot, hoping that it would simplify some analysis. I work with two large tables for an account management scenario. One table contains a row of detail for each instance of service provided in the past year. Another table contains a row for all instances of customer feedback and incremental purchases by the customer. The common fields across both tables are Employee Name and Customer Name.

When I try to link them in the diagram view, I get the error "The relationship cannot be created because each column containes duplicate values. Select at least one column that contains only unique values."

Obviously there are many duplicates, since we have a dozen account managers servicing several hundred customers with several interactions each during the year. I was hoping to summarize/analyze the linkage between types and volume of service vs. incremental sales. Am I mistaken to think that Power Pivot would be helpful in this regard? Is there another approach? Thank you.