I've seen some posts that seem to indicate that it's when the price says "not available for purchase", but that doesn't seem to be 100% accurate - I requested an item that was not available for purchase but it gave me the message saying it's been less than 30 days since my last review. Then I noticed that it didn't have the "presented by" label on its product page. Is that the more foolproof method of telling if a sponsored review is available?