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Two questions cover most of the risk. Is the piece officially licensed, and is this the exact version you meant to buy? Licensed goods carry the rights holder's marks and a manufacturer product code on the packaging, and that code is what lets you check a listing against the maker's own catalogue rather than trusting a photograph.
The second question is about where it will live. A collection on an open shelf ages differently from one behind glass, and mixed collections need the most planning, because a 25-centimetre figure and a row of keyrings want neither the same shelf depth nor the same eye level.