Never Trust a Thief! by Robert Silverberg — Read

Kiley felt all-powerful with the alien guiding him in the looting of a world. Now the whole galaxy was his if he could remember to --

Kiley took one last, fond look at the glittering heap of jewels in the back of the spaceship, nodded happily to himself, and began to set up a blastoff orbit. Somewhere down on the field far below, he could see dot-like figures -- spaceport attendants, all firmly convinced that this was an authorized flight.