Rust! Should I sell it?

The underside rust might look worse than it is from the paint bubbling. You won't know until you wirebrush the loose stuff off. Car shows often strip everything and send for a full acid dip. Even L.A. car bodies come back showing some pinhole rust-thrus. But, that is a $$$$ restoration. After wire-brushing, I soak in Evapo-rust, using rags and plastic sheet to keep body panels wet for a few days. Wire-brush again, then repeat with phosphoric acid (in all rust products) which converts pits to hard black iron phosphate. Buy it cheap as Concrete Etch at Home Depot. Wire-brush again, then a good primer.

As mentioned, the package tray rust-thrus don't have to be repaired since the trunk to cabin is not air-tight. But, it likely indicates rainwater intrusion from poor sealant or rust-thrus around the rear windshield, so I would pull it. Don't try to pry the glass out of the gasket (my mistake, shattered), rather remove the gasket with glass, pulling to the outside. Alternate, at least pry up the rubber gasket to clean and seal with either elastomeric caulk or rolled butyl rubber (used to seal trailer windows). They may extrude out over time, which is good (assured fill). Just cut it off flush with a dull putty knife. To do well, you must remove the stainless trim (watch youtubes, special pliers to release clips). After that effort, you'll likely decide to remove the glass-gasket.