Scouting turns a table of 500 books into a filterable database. Most resellers set a minimum profit and rank threshold in the app, then scan quickly and keep only the triggers, which is far faster than evaluating titles by knowledge alone.
Etiquette and rules matter at library sales. Some Friends groups ban scanners entirely, others ban them during preview night only, and nearly all expect you to stay out of the aisle and not block tables. Ignoring posted rules is the fastest way to get a sale to ban devices for everyone.
Scanning has limits. Books published before the mid-1970s have no ISBN, and many collectible, signed, and out-of-print titles will not scan usefully — which is exactly where knowledge-based picking still beats a device.