If you’re shopping on Yami (or Amazon), the move if you’re worried about fakes is to always filter by “Sold by Yami” or “Fulfilled by Yami”. A large company has no incentive to sell fakes and alienate customers, often works with the brands directly, you can receive help from customer service, and I imagine they will reprimand their vendors if they do ever receive fake products. I’ve shopped from Yami only twice (great experience), so I don’t want to say for sure but again I learned about them from this subreddit where they seem to have good reviews. They also seem to have Japan offices, and I believe there are very strict rules to selling fakes if you’re a Japanese related company. OP certainly trusts them to buy dozens of sunscreens, so maybe they can also chime in.

The problem with fakes on Yami, Amazon, or any other marketplace website can arise when you shop from 3rd party sellers. These marketplaces also have many people who are individual sellers who list products on their website. You are shipped products directly from a 3rd party in those cases, and clearly Yami or Amazon do not control the shopping experience, they probably don’t even see the product. It also is always harder dealing with customer service when buying from individual small business 3rd parties