The student pilot stated the airplane was for sale. A commercial pilot had arrived at the airport to look at the airplane. The commercial pilot asked if he could fly the airplane. The student pilot got into the back seat and the commercial pilot got into the front seat. The student pilot was flying the airplane. They flew over and circled the State Park. The commercial pilot took over the controls and headed back towards Beltsville at 2,500 feet. The student pilot stated that the commercial pilot "was flying the airplane fairly slow and making some easy turns. The airspeed seemed to decrease a little" and the student pilot said the commercial pilot "started a left turn at a slow airspeed. the left wing dropped, the airplane stalled, and entered a flat spin." The student pilot "took over the controls, applied power and opposite rudder. The airplane would not recover. The airplane collided with trees and the ground." The commercial pilot exited the airplane first and assisted the student pilot out of the airplane. They both walked through the woods and came to a highway. They walked over to a gas station and they asked the attendant to call 911 and tell the 911 operators that the pilots were ok. The student pilot then went home to see his girl friend and children. The commercial pilot went to the airport and departed. According to the commercial pilot, he spoke with the student pilot on the morning of the accident and informed him that he would fly in around 1200, so that he could see the airplane. He informed the student pilot that he did not have any tail wheel experience, and that the purchase of the airplane would be contingent upon his being able to store the airplane at his hangar. The commercial pilot stated that the student pilot demonstrated the airplane and then let him take control. Then the student pilot took the controls back and we just flew around and then he brought the airplane up into a stall. We came out of the stall and just started spinning straight down. I thought to myself, "when is he going to get us out of the spin? and I looked down at the controls in the cockpit and he had full left stick, full right stick, full forward, full aft stick; he brought the power back on the engine and the plane just kept going straight down, there was nothing anyone could do. We crashed through the trees and hit the ground." fortunately, we were able to walk away. According to the commercial pilot he was not made aware that the student pilot was not a certificated pilot. In addition, the student pilot did not provide a completed pilot/operator report as requested. Examination of the airplane by an FAA Inspector found substantial to both wings, the airframe, and the engine. There were no mechanical problems reported by the pilot or discovered during the post-accident examination of the airplane.