Large international buyers play a key role in global value chains. We exploit detailed transactionlevel data on the usage of material inputs to study how Bangladeshi garment suppliers' markups vary across international buyers. We find substantial dispersion in markups across export orders of a given seller for the same product. Buyer effects explain a significant share of this variation, while destination effects do not. Buyers adopting relational sourcing strategies pay higher markups than non-relational buyers. This pattern holds within seller-product-year combinations, is robust to controlling for the buyer's size, traded volumes, and quality, and, together with larger volumes, implies higher profits for suppliers dealing with relational buyers.