Is selling used books on Amazon still worth it as a side business?

for a one-off 400 books, fine. as a business, the margins are thin. scan every one with the Amazon Seller app before you list anything. most common paperbacks sell for a penny or a few dollars, and once the referral fee and the extra closing fee on media come off, those lose money. the ones worth listing are textbooks, niche non-fiction, technical stuff and older out-of-print titles. from a house clearance, maybe a fifth of them are worth the effort. FBA makes sense for the better books only. the cheap ones cost more in fees and inbound shipping than they sell for. what's left can go to a local charity shop or in a bulk lot.