I know I am late but I would add that in EVERY case your homework should be done and NEVER buy anything with out documentation from a dealer with a perfect reputation. Also I understand that there is a huge market for them but personally I do not care for "paper props" (news papers, photos,flyers,etc.) Too easy to copy.
Super popular props: Holy grail, hoverboards, Freddy gloves, and the like are dangerous due to the amount of fakes and legitimate replicas out there. I would rather have a well documented Mangalore rifle than a questionable flux capacitor!