A product catalog service allows merchants to create and store product catalogs indicating products that are available from the merchants. Transaction data from point-of-sale (POS) devices of a plurality of merchants can be received. A first catalog of a first merchant can be obtained from a first POS device of a first merchant. The first catalog contains items to be sold by the first merchant. Using the transaction data and the catalog, a second catalog of items to be sold by a second merchant can be generated or updated and transmitted to the second merchant. Items can be compared using item attributes. Item descriptions in the second catalog can be based on item descriptions in the first catalog.