John,
I see one of the ones that you are talking about ("pulled from Training Department") and it does appear to be in excellent condition; it may, indeed, have seen little use, based on the condition of the card edge fingers and the BNC connectors. Given the location of the seller I think it's certainly possible that it came from a Tek site. I wonder what kind of training it would have been used in where it would have gotten so little evident use. I also wonder how long ago it was pulled from that environment.
It's being offered as "used" which should give you some protection (or recourse) if it is not working. I don't think that the price is unbelievably low. Have you gotten pictures of exactly the item you would be purchasing ? Given that it says there were five available, and only a single serial number is shown in the pictures, I would worry that the others were not in similar condition.
If I were in the market for another function generator, I'd probably buy it, but I have a weakness for TM500 stuff.
-- Jeff Dutky