 Why is Retief so concerned about the tractor order?
I'll leave him to you, Retief," Magnan said. Arapoulous puffed on his cigar, looked worriedly at Retief. Retief put aside his cigar, pulled the wires loose, nudged the cork, caught it as it popped up. "Boge is a troublemaker, so every agency in the Corps is out to pacify her. Why, most of d'Land's difficulties are due to the unwise trade agreement she entered into with Boge. Retief saw them lined up on the ramp waiting to go through customs.
 Because the order of tractors is unusually large.
 Because he knows whoever ordered the tractors has bad intentions.  Because he knows the order is a mistake.  Because the order of tractors is unusually large.  Because no one else appears to be concerned about the tractors.