That paperback book you ordered from Amazon for your upcoming beach vacation might just arrive faster than you thought. But it’ll come at a new cost for the third-party seller providing the title: Amazon is once again tightening the reins on sellers who don’t use the company’s fulfillment services, reducing their required delivery window.

Just days after Amazon changed the way returns work for third-party merchants — bringing the experience more in line with Prime services — CNBC reports the e-commerce giant is making a similar change to the way the sellers who fulfill their own book, CD, and DVD orders deliver the goods.

Get It There Faster

A recent email sent to third-party merchants revamps the timeframe in which these sellers are required to deliver orders, starting Aug. 31.

Instead of allowing sellers four to 14 days to deliver orders, the company now requires orders to be delivered within four to eight days.

A rep for Amazon tells CNBC that the change was made as the company launches new capabilities to help set faster delivery times for seller-fulfilled products.

Amazon seems to believe that the change will result in more customers for these sellers, as it notes that shoppers are more likely to purchase a product if it has a faster delivery estimate.

Rising Costs

While…