For book sellers, FBA matters because it makes listings Prime-eligible, which typically supports higher prices than merchant-fulfilled offers on the same title. That price gap is often what turns a 50-cent library sale book into a worthwhile flip.
The cost side is real: per-unit fulfillment fees, monthly storage, long-term storage surcharges on slow inventory, and prep requirements such as polybagging. Books that sit for a year can quietly cost more in storage than they return.
This shapes what you buy at a sale. Heavy books, oversized art volumes, and low-rank titles carry more fulfillment and storage risk, so the profit threshold for taking them should be higher than for light, fast-moving paperbacks.