The suspect, named by police as Riad Lahkin, 37, went to a 7-Eleven store in Sirirat Road, Patong, about 5.30am.
He told shop assistant Sunisa Mornlamai that he had bought a mobile telephone at the store for 1200 baht and it didn't work so he wanted his money back.
She said he'd have to wait for the manager to start work later in the day.
He left the shop, then returned a minute later, grabbed a pair of scissors from a display, and threatened her with them, police said.
She gave him 2000 baht, he fled and was arrested soon after at Lucky Mansion by patrol officers.