The discount store behemoth has always had a reputation for demanding lower prices from vendors but Reuters has learned from interviews with suppliers and consultants, as well as reviewing some contracts, that even by its standards Wal-Mart has been turning up the heat on them this year. “The ground is shaking here,” said Cameron Smith, head of Cameron Smith & Associates, a major recruiting firm for suppliers located close to Wal-Mart’s headquarters in Bentonville, Arkansas.