It takes him a minute. He's got to stare at yet another flying person first. How do they do it? This one doesn't even have wings!

When he's done staring and remembers to close his mouth, Luke practically dives behind the sales counter, checking shelves and drawers and most especially the floor. There's a worn throw-carpet back there, presumably for the cashier to stand on; looking under there is so obvious it's probably not going to do anything.

He's checking anyway.