Legitimacy

hi, if you're planning to buy something online, first thing first, make sure you buy from trusted seller that only sells authentic products. maybe you could find brand's online shop or from big retailers like Sephora or Watsons, whatever available in your area. if you already bought the product, some brand does have hidden tag on it or some kind of sticker you could verify. unfortunately, I don't think cosrx had this feature on their product (well, not on three products I purchased from them) so it's best to choose the seller carefully.

some brands have really complicated holographic stickers that are hard to counterfeit but this is usually the more expensive brands, as a rule I avoid buying things on Amazon and eBay to reduce chance of fakes

You can check cosrx’s Instagram to see who their official sellers are!

Oh, i don't sure how to check it but it would be easier if you're buying the products through their official website. Nowadays, it's really easy to get cosrx products. You can buy in here: 💛cosrx official website 💛shopee/lazada mall 💛yesstyle 💛style korean and etc. Hope this will help you