This site's own buyer checklist lists this specific fifth step — worth understanding it on its own.
This site describes it directly: contact the seller directly if label information is unclear — worth reading this as this site's own direct solution to the ingredient-verification gap it couldn't resolve itself.
S. Whitfield's featured quote specifically describes doing exactly this — asking the seller directly about the ingredient list and getting a straightforward answer — worth reading that account as a real-world example of this step in practice.