Already mentioned but here are some more areas to check for rust :
Rear hatch under/around the dust/wind deflector mounts and around the gasket (rust or rust "bubbles")
Rocker panels (below the doors), particularly the rearmost section, need to get on the ground, look and feel up
and behind the running boards which tend to hide the rocker panel. Check the back (inner) aspect of the rocker
panel cavities also.
Front fenders; check the lowest aspect closest to the front doors including the underside where there are a couple of bolts
Rear wheel wells, both the front lower aspect next to the rocker panels and the rear lower aspect next to the Quarter panels
Quarter panel bottoms, check outside by looking up (bumper caps get in the way) but also check inside by removing the cargo area panels, take photos looking down into the cavity. If you see a lot of caked/dried dirt there's likely a rust hole somewhere (or missing grommet) letting it in.
Check closely around the windshield gasket, look for rust "bubbles", that often means there's a hole in the metal.
Inside lower edge of all the doors and lift gate, lift the weatherstrip rubber to get a good look, rust often starts under the factory seam sealer.
Also around the inner edge/lip of the hood (seam sealer area)
The roof is roached, will need to remove the roof rack and the headliner then have metal welded in to fix it right.
The vehicle obviously has been painted with a color change, looks like it was green originally, so you need to check extra closely for rusty/damaged areas that may have been covered up or had quickie bondo repairs.
Any rust can be fixed just need to find a good body shop but it won't be cheap to do it right.
FWIW