I'd wondered if someone would raise the issue of whether I ripped off the buyer. At one time, back when Shutterbug was printed on yellow paper, camera collecting was a much less visible hobby, and information about market pricing was difficult for the lay-person to find, I think that may have been a legitimate question. But in today's world, as has been noted above, all you have to do is google "Noct-Nikkor" to find a ballpark value in seconds.
Did the seller do that? I don't know. Perhaps he did, and decided he just wanted to sell the camera. Perhaps he knew he could do the search, and didn't bother to do so. Perhaps he didn't make any effort and simply pulled a price out of thin air. I do know that he was selling a variety of other photographic items, so was not someone with limited experience of camera gear.
I'd like to think that in different circumstances, with a person less web-savvy, I'd offer a price that reflected my perception of the value of the item and my ability to afford the purchase. In this instance, the seller was educated, web-connected, and set a price -- I respected his right as an adult to do so.