I have come to believe that the verbalized condition of rust is geographical.
I bought my Standard Vanguard on Ebay. I had a guy from the St. Louis Triumph club look at it. He said it was "pretty rust free".
When it arrived in California, I noted paint blisters and rust on the door sills, and when we got it on the lift, there was a patina of rust on the whole underside.
I just there's a difference between California "pretty rust free" and Missouri "pretty rust free".
The rule is, go look at it yourself. But with this case, I guess you don't need to.
And another thing...
Sometime I think that some of these guys are selling to the uninitiated in vehicle restoration. I've seen several ebay offerings that bragged about how well the car ran despite the body damage or rust. Emphasize the positive! Don't let the poor sucker know that sheet metal is the most expensive part of restoring a car.