What Doug just said, plus the provenance of an item is essential as far as getting to the comfort level to spend the amount of money that we're talking about. If you see anything about the provenance that seems inconsistent, simply walk away and look for a different collectible.
To quote Jim Stinson, one of the really good guys on the autograph side of our hobby,
"the most expensive purchase that you will ever make is the one that is not (genuine) real". Solid words to live by as a collector.
The fact that you did the amount of research that you did prior to your initial post shows that you are already thinking clearly when considering adding an item to your collection.
