When was this domain registered?
Straight from the registry record, free, no account. A store selling a brand that has traded for years, on a domain created a few weeks ago, is the single fastest signal there is.
One signal is never enough
Age matters in combination: a young domain that also serves product images from the real brand’s own content delivery network, reuses its page title, and has policy pages that error. The full set is in how to check if a store is real.