I've been studying this phenomenon of sellers understating the problems with their Airstreams, and come to a few conclusions:
1) Most sellers don't really know their Airstreams that well. If you want to trust the seller's claims about condition, look for someone who actually uses their Airstream regularly and is an enthusiast (WBCCI member, forum member, etc).
2) "No leaks" is about the most worthless promise you can get. What it often means is, "I haven't seen the leaks yet," especially on vintage trailers. My favorite was a recent eBay listing where the seller said something like, "There aren't any leaks worth fixing." (In reality, there aren't any leaks you can safely ignore!)
3) Other dangerous phrases uttered by sellers:
-- "ready to go camping!"
-- "good for hunters" OR "I used it as a hunting camp"
-- "haven't had time to use it in the past XX years"
-- "everything works"
-- "I never used the XXXX so I don't know if it works" ( = it doesn't)
-- "I fixed it by XXXXing it, but it will need further repair."
-- "I don't have any more pictures"
-- "mint condition"
4) A lot of people think "vintage" means "valuable." My motto is, When you run into a seller who is convinced that their Airstream/Argosy is worth a lot just because it's pre-1978, run the other direction!
I experienced this with a seller who claimed "excellent" and "mint" condition. I guess that could be true if the mint makes them with dead mice in the cabinets, smells emanating from the toilet, mold in the fridge, dented cabinets, broken tambours, faded upholstery, rusty tongues, and weeds growing through the rear storage compartment!
(It would have been funnier if I hadn't driven 300 miles to experience it personally.
) But the kicker was that the asking price was nearly $5k -- because it was "vintage."
6) And finally, ipso facto, I must disagree with your earlier statement. Most Airstreams are not truly rare. I do agree that they are "desirable" but that's entirely different.
The rare Airstream is the one that has been lovingly cared for by its owner and remains in excellent operating condition. Junkers, on the other hand, are readily obtained on eBay any day of the year.
Caveat emptor! and use the Volunteer Inspector list posted on this forum if you decide to buy another Airstream/Argosy out of state.