... The intent is key. If you make an exacting replica of something that is fabricated like the original (like early "Mark English" ST TOS replicas), then you're at least honestly making a replica, but the conditions under which you sell it can be critical. If you then age, weather, or otherwise distress your replica to pass off as a potential screen used (or just original propmaker's inventory) prop (that I understand "Mark English" later did) and sell it with or without a claim as to the piece's provenance, you could be accused of making a forgery IMHO.
The replica maker who incorporates "tells" (hidden or clearly in view) is arguably insuring AGAINST the accusation of producing a forgery. I don't think it's asking too much for this.....
Forgive me on this, but I like to play Devil's Advocate...
I have a particular Airsoft gun.
It's the exact same model from the same manufacturer as used in a movie. Does that therefore equate to me owning a 'forgery'?
I don't see how something made from, say, found parts by a prop maker, which is then copied using the same methods and parts by an enthusiast equates to a forgery unless the enthusiast claims it to be the original.
... Also, why does the buyer not have to reiterate that it's a repro when selling something on? Or at least state that they don't know either way?
Surely unless they have certification, it's to be assumed as a repro?
First off, Devil's Advocates
never ask for forgiveness.
If you have the same Airsoft gun that some filmmaker used, no it's not a forgery, it's clearly a commercially available Airsoft gun. End of line. It probably has the manufacturer's marque right on the gun. Duh.
If you take that Airsoft gun and add resin and plastic and paint markings to closely match what was done for a production (e.g. Bruce Willis' gun from FIFTH ELEMENT?), then what? If you idealize it (make it better than the propmaker did, or don't distress it like the production prop was during use) is it a forgery or a replica?
All kidding aside, what I meant, and you can read again, was "intent is key." If you reproduce a light saber from the same authentic parts that the 1976 propmaker did, are you making a forgery? Probably not. If you weather and age it, put in scratches that you can see the original has, are you making a forgery? Arguably yes, but just as arguably not if you insist you're just making "a replica of the real prop as it appears today." How you sell it, and describe it, can make a big difference. Reference the suit against Christie's and IIRC Paramount by the owner of a "screen used poker visor worn by Brent Spiner," who subsequently learned that it is at best one of several used on the production. He seemed to think he was getting a one and only costuming piece, and was dismayed to find it was not. How did Christie's describe it? QED.
You raise a good point. If a reseller presents it without a COA confirming the source of this prop is an original production prop, and says, "provenance unknown," or words to that effect, is it misleading? Only IMHO to the buyer who deludes himself/herself. But if the seller says, "possibly original production prop, no COA offered or provided," is the buyer still obligated to be skeptical, or is the seller misleading. Again, if the replica maker puts a tell or mark on it indicating manufacture later than the production, the point is moot. A couple of recent Ebay auctions of "original Star Trek props" are fine examples. Sellers said things like, "the lady we got this from thinks it's from the production, we don't know either way," or "estate auction from a collector known to have bought screen-used originals," or "think this is a stunt prop from the production, but I have no way of knowing." In these cases, I was able to identify two of them as replicas based on identifiable tells (that even a n00b like me could see), and two sellers backpedaled. The third dunsel refused to quantify any doubt, and couldn't sell the "unpainted resin stunt prop" for $49. :unsure
Please, don't let your imaginations run away here. I'm not proposing gashing your masterpiece up with a Diamond Deb file, or printing in 24pt font "REPLICA" on the face of an ID card. A small mark like silversmiths put on cutlery, or a 6pt notation, in an inconspicuous place is sufficient. A maker here of a James Bond credit card has valid dates 07/07 - 07/17. Unless CC's have 10 year spans in the UK, that's a pretty good tell that it's not a real CC.