Looking At '04 XLS

[Gtody]

I am looking at purchasing my first Explorer. It is an 04 XLS with V-6. Car Fax says it did not pass the last emissions test. That is not an issue where I live, but what would be the most common cause for this? The car has apprx. 97,000 miles on it. What other issues should I be looking for?

Thank you.