I need your help to determine if my copy of Link to the Past is a repro.
Appearance-wise, sure, it looks like the real deal, but, as
redblaze57 pointed out, you need to look at the board; otherwise, there's no way to accurately tell.
A rule of thumb you should follow whenever buying cartridge-based video games off the Internet is to always make sure that the listing has photos of the game in question, with at least one of them showing the board; the listing also having a proper description should also be taken into account. Never buy cartridge-based games from sellers who only use stock photos or just have one of the front and back of the cart, especially if you message them looking for additional information and they lack the common decency of replying. To be frank with you, straight up ignore any seller who not only doesn't have proper pictures attached to their listings but also lacks an adequately written description of the items they're trying to sell. By that same token, don't waste your time and energy if you come across a listing lacking a description, more so if all there is is a note by the seller telling their potential buyers to do the legwork and message them for information, because chances are if you bother with such a listing, you're going to regret it. And, even though I think it goes without saying, make it a habit of taking a few minutes to check their feedback. Now, keep in mind that this doesn't apply to all cartridge-based games, as Nintendo DS and 3DS games, for example,
require you to essentially break them apart to get the board out. So, if you ever were to get a copy of Pokémon Platinum, just to name an example, your best bet is checking
gameverifying over at Reddit, although there's also
this for that specifically.
All in all, stick to eBay; you're better off there as a buyer than a seller anyway. If you can't find whatever you're looking for, then just be patient.