Masks, water filters, power banks and branded batteries are often faked. On Lazada buy from LazMall stores, on Shopee from Shopee Mall stores (official brand shops), or from a big retailer.
Preparedness
Warning signs of a fake or unsafe product:
A price far below the other listings (for example a famous-brand filter or mask at a fraction of the usual price).
A seller that is not the brand's official shop, with few ratings.
Missing certification marks (N95 / KN95 / P2 on masks; the Thai TIS mark on power banks) or blurry printing.
A power bank that is much lighter than a genuine one of the same capacity.
Safer choices:
LazMall (Lazada) and Shopee Mall (Shopee) list official brand stores and authorised sellers.
Big retailers (Makro, HomePro, Global House, Boots) sell through their own shops.
Keep the receipt, check the product on arrival, and test power banks and radios before you need them.
Why it matters for Koh Samui
A fake mask does not filter haze, a fake filter can let bacteria through and a fake power bank can overheat. In an emergency you only find out when it is too late.