Could be a good deal. I see substantive rust on the body of the rear hatch by the handle. Leads me to believe there is much more on this vehicle as that is not a super common rust area. They just replaced the exhaust system and gas tank - further signs of rust issues.
There may be body damage to rear driver door so inspect that. Would very carefully inspect the underside, including behind the rear wheel well covers where it meets the rear bumper cover among many other areas.
The $9k in maintenance they are noting is fine, but if they paid that much for exhaust, brakes, and tires they got absolutely hosed, or it was a nightmare job...because of rust.
Could be a great deal but my gut would say to exercise a lot of caution. It's rare someone is super motivated to sell a vehicle they just out $9k into, for $6k.
I think it's likely they are passing along a serious set of issues and major deferred maintenance to the next buyer. The period from 180-220k IMO is the most expensive period to own a 100 series from a maintenance perspective, even with zero rust.