The commercial pilot, seated in the left seat, reported that he lost directional control of the tailwheel-equipped airplane while landing, resulting in a ground loop. The flight instructor, seated in the right seat, was providing an aircraft and local area familiarization flight. During the ground loop the airplane’s left wing struck the ground, and the main landing gear collapsed. The airplane received substantial damage to the wings and fuselage. Neither pilot reported any preaccident mechanical issues with the airplane.