The mural by the famous graffiti artist was painted on a 9x8-foot section of brick wall at a gas station in Hollywood in 2008.
Eytan Rosenberg, the gas station owner, says he had never heard of Banksy. He was approached by the street artist and a friend for permission to paint on his wall.
"He introduced himself, I shook his hand," Rosenberg said. "I was busy, didn't really take much more time, went back to work."
Later, one of his employees called to say that the gas station had been tagged with graffiti, so Rosenberg told him to paint over it immediately -- until he recalled the conversation he had with the two men.
"So I called him back and said, don't touch it!" Rosenberg said of the employee. "It almost got painted over. I ran down to the station. Before I even got there, there had to have been 50 people taking pictures of this thing."
Rosenberg had dozens of security cameras aimed at his family's gas station, but the tape was mysteriously blank when Banksy was working.
"Flower Girl" will be one of five auctioned pieces that Banksy created on plywood and concrete walls and doors in Berlin and London.
The Associated Press contributed to this report.