The pilot in the right seat of the tailwheel-equipped airplane reported that, he had just sold the airplane to the pilot in the left seat. The right seat pilot was on the controls, and during a wheel landing, the airplane encountered a wind gust from the right. The airplane veered right, and he "apparently over-corrected," to the left. The airplane exited the left side of the runway and the right wing struck the ground. The airplane was not equipped with brakes on the left seat pilot's side. The airplane sustained substantial damage to the right wing spar and aileron. The airport's METAR reported that about the time of the accident, the wind was from 290° at 10 knots. One hour prior to the accident, gusts were reported at 17 knots, and one hour after the accident, gusts were reported at 20 knots. The pilot landed on runway 21L. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.