ZHANGJIAGANG, China—When the U.S. raised its tariffs on Chinese imports in May, Harlan Stone knew his U.S. vinyl flooring importing business had to move fast.

He got on the phone with his main customer, Home Depot Inc., to update it. Soon he was on a plane to China, prepared for tough conversations with suppliers.

Mr. Stone cajoled his Chinese suppliers not to let the now-25% tariff deter them from the American market. He worked across time zones to see if Home Depot would absorb part of the added costs. He tried to time ocean shipments so that some might not be subject to the punitive levies. And his U.S. team looked at rejiggering transport and packaging costs for more savings.

“It comes down to every little thing,” said Mr. Stone, wearing sneakers and a Yankees cap as he moved between meetings in the Yangtze River port city of Zhangjiagang. "We find every quarter-point we can. If you have 10 quarter-points, then you have 2½ points.”

When the Trump administration first imposed 10% tariffs on many Chinese goods about a year ago, suppliers, importers, distributors and retailers worked together to defray the cost and try to avoid passing it on to consumers for fear of losing sales. Mr. Stone and his Chinese partners initially ate most of the vinyl flooring tariff cost, passing just a tad on to retailers.