Dear Wannabe,
No disrespect to you, but here is some really good advice, from an experienced (and previously burned) antique firearms collector.
If you are interested in buying an antique rifle (particularly a very expensive one like the Winchester 66), and you find it necessary to ask even a single question about how to determine its condition, then you simply do not know enough about that type of antique firearm to be buying it, and you will get burned, cheated, every time! If you miss or overlook or misjudge even one small factor about that firearm, then you are very likely going to pay $7,500 for rifle, that is only worth $4,000.
You must spend years studying everything out there about the Win. 66, and going to every gunshow you can, and handling and personally inspecting every one you can, for years, before you can even consider buying one, unless you just plain want to get cheated.
And, go to the bigger shows, and find an older guy who has lots of top quality Winchesters, and just start asking him collecting questions, making it clear that you are not interested in buying but just learning. Most of them love to pass their knowledge along, and to give you an on the spot seminar about anything you want to know, even pulling out several rifles with different finishes, conditions, defects, etc. and showing you how to tell the small differences.
Once you have trained your eyes, by inspecting hundreds of different examples of the firearm, then believe me, you will have no problem whatsoever in spotting a re-blue or other such factor. For some reason, the piece just looks "wrong."
Hope this helps.
Mannyrock