The seller doesn't sell too many ancients, so he's not going to be an expert at picking fakes (and even the experts get fooled sometimes). For $5, you can't go too far wrong either way, and Constantines are a nice cheap series for the beginner - I'm trying to put together a full mintark set. But $5 does seem a tad too cheap for a genuine Constantine in that condition.
On the other hand, it's not an obvious fake to me. The only "worry" with me is the neck, or rather, the lack of a neck. Where'd it go? [:p] Lack of "low point" detail like that could be a sign of a cast job.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis