Look for the answers to these questions.
Does the PO have any metrics to look at?
How are they relevant? Money in the bank?
Fewer bugs (reported from in-production systems)?
Only high-value features in the product? Decreasing the code base?
Anyone can cram things into a backlog and a product, endlessly building things that may prove useful or valuable (or not). A successful PO needs to know how to validate their business assumptions, or at least have an idea (put into practice) on how to do a quick and easy validation of business assumptions.