Police said the latest robbery took place at the Lotus Express Ban Thon branch on Udon-Kudjub Road in Tambon Ban Luam.
Two cashiers told police that the robber, who concealed his face in a full-face motorcycle helmet, walked up to the counter and raised his hands to give a wai, then said he wanted to borrow Bt1,000.
The staff said the man had a knife in his right hand and he also lifted up his shirt to show a pistol in his waistband.
After staff opened the cashier's machine and handed out Bt1,000 he raised his hands and gave another wai as a gesture of thanks and sped off on a motorcycle driven by another man.
Police suspect that the same thief robbed another Lotus Express about one kilometre away on December 13. The robber also asked politely for Bt1,000.