As with so many of these neglected old bikes, one should remove and carefully inspect the wheelset if possible before deciding on a value to be willingly paid.
With deflated and deformed tires with the rim strips hanging out, one finds it difficult to discern if any rim damage has occurred.
Having to replace the wheelset or spend hours fixing this one part of the bike affects the value that you could ever get out of the purchase.
Look for rough axle bearings or flat-spotted rims in particular, then move on to inspecting the rest of the bike.
For occasional or light use, not every bike needs a proper rebuild, the oil-can tune-up often is fine for limited service! So inspecting the present state of the assembled headset and bottom bracket will also help determine the bike's realistic value.
Lastly, without being able to ride the bike before purchase, examine the bike's visible frame alignment the best that you can, looking for any sort of asymmetry, cracked paint, dents, cracks, bends, etc.
And don't neglect to check for a seatpost or stem frozen into the frame. Hours can be wasted there, and in extreme (but not uncommon) cases, parts might need to be cut out with a saw blade.
This post came out after hours of work over several week's time, but as a result I realized that I simply paid too much for this old, mid-level bike. The wheels also turned out to be throwaways, and I still haven't been able to source proper decals for it after another year having gone by, so a valuable lesson has been learned.
