So, they know it is reblued but chose not to mention it?
Welcome to Gunbroker. You'd be amazed at the number of "collector" rifles which get listed (and sold) with major/obvious issues not disclosed in the description.
Sometimes it is a crooked seller, but more often I believe it is a result of a seller who is not fully aware of the problems themselves. The sellers frequently are not collectors, but are the unwitting pawn shop employee who has done 10 minutes of research on the internet and concluded they have a rare and collectible rifle on their hands. When this happens, the lister honestly has no idea about things like modifications or rebluing.
Also, there are a lot of people who believe rebluing a rifle makes it more desirable, not less. They can't fathom that a rifle would be worth more in a mottled brown patina than looking brand new with a fresh bluing job.