I completely concur with Kevin.
Here are a few other things to look for and consider:
The axle is 20 years old. An upgrade with brakes
could cost up to $750 installed.
Is the refrigerator
in good working order?
Check the door fit for a good seal. Repairing these can be a big job.
Look for any evidence of silicone around the windows
or roof vent (anywhere, actually!) This would indicate a prior (or current) leak.
Is there ANY indication that water may have seeped to the floor...?
What's the general condition of the shell? Lots of oxidation? Are the rivet caps intact? Any loose rivets? When I got my 1988 Scamp last summer, the gelcoat was beyond repair and many rivets were loose. (I replaced all rivets with SS nuts and bolts, and had the shell professionally painted.)
If all is good with this camper, and depending on overall quality (and your desire), $3000—5000 is in the range of reason. But if it needs any of the above, you have room to negotiate. And if they're selling for less, even better for you!