Glen,
It does sound a little fishy, but the price is on the high side of for an "as found" Airstream for a '75 27' Overlander.
Price vs. Condition - Airstream Values
If you have a WBCCI membership book you could do some research on the membnership numbers "17314". I would look them up, but I am at work right now.
Also the stars next to the WBCCI numbers denote 5 years of membership / star, so this is a 20 year member.
Just remember, if it sounds too good too be true, it probably is. I would have to say pass on this one unless you can verify all this information and physically inspect the trailer,