I purchased brand-name cosmetics, but I think they may be fake.

The manufacturer who holds the copyright on the brand can determine whether the product is genuine or fake. But usually manufacturers do not accept requests to verify product authenticity. Therefore, it is not easy to confirm whether or not what you bought is genuine. Some manufacturers will only sell their products at authorized stores. If you want to avoid the risk of buying fake products, it is recommended that you shop at an authorized store.