The sales you don’t make
Do a search on great jazz singer "Emily Barlow" in Amazon and you'll find… nothing. That's because her first name is spelled Emilie and Amazon gives up.
Do a search on Lord of the Flies and you'll find tons of matches, but none of the top ones are for the book–they're all for expensive annotated or educator's editions. Broken search = no sale.
It's extremely difficult to figure out why people walk out of your store, throw out your brochure, leave your site… but in fact, this is fertile territory for dramatically increasing sales. You won't find what's broken if you don't look.