The pilot was undergoing a check flight with an instructor, as he was contemplating purchasing this type of aircraft. This was the first occasion that the pilot and instructor had flown together. A series of exercises was carried out, during which the pilot was asked to demonstrate a power on stall at a height of approximately 500 feet. During this exercise, the pilot did not lower the nose sufficiently during the recovery. The pilot was not accustomed to practising stalling at such a low altitude, and during his previous training this had been carried out at 1500 feet. After some discussion another stall recovery was carried out, and on this occasion the pilot used the correct technique. The instructor then decided to return to the strip to carry out some circuits and landings as he assessed the pilot to be unsuitable to fly solo. The flying technique required by the instructor was generally at variance to that previously experienced by the pilot, and it would appear that the check flight was rather vigorous without the opportunity to become accustomed to the environment. During the return flight, the instructor described the circumstances which could cause the aircraft to stall during a forced landing with no power. To demonstrate this, he then closed the throttle at a height of between 300 and 500 feet, and asked the pilot to adopt a glide attitude, initiate a stall and then effect a recovery without the use of engine power. The pilot did not lower the nose sufficiently after the stall symptoms appeared, and he was told to further lower the nose, as a steep nose down attitude is required to effect this type of recovery. When the pilot did not commence to ease the aircraft out of the ensuing dive, the instructor called that he was taking over, but he was unable to move the controls. The pilot had become rigid at the controls, the instructor was unable to correct the situation, and the aircraft remained in a pronounced nose down attitude until ground impact.