My first question would be, what's the provenance? If you can't answer that question well enough to convince someone else, you may have a VERY difficult time reselling the piece. And as much as we'd all like to think we'll never have to resell something, I just sold my "holy grail" of screen-used props because I needed the money more than an expensive collectible even though it absolutely killed me to do it.
If you're getting it through a relatively trusted seller like Screen-used or the Propstore, you're probably safe.
If you're getting it from some guy who knew some guy that got it from some guy that got it "directly" from the movie set, I'd be very, very careful.
You've got to approach screen-used prop buying with a VERY skeptical eye. Don't fall into the "I want to believe" category so many others do...
If you've got an account on the movie prop forum, that'd also be a good place to ask your question.