The commercial pilot, (CFI), was performing a rental checkout for a private pilot with one passenger on board. The CFI said he used 10 degrees of flaps for takeoff, lifted off at 56 knots, and climbed at 67 knots. These procedures are not in accordance with the aircraft operator's manual for normal nor short field takeoff. He reported that the plane would not climb above 50 feet AGL. The flight area is over city streets, and has powerlines and phone wires every block across the route of flight. The CFI said he pulled back on the control yoke to raise the nose, to clear wires. The plane began to lose altitude. He said he retracted the landing gear but struck wires during this attempt to clear them. The CFI made a forced landing in a field. He said he lowered the gear, retracted the flaps and at touchdown, the nose gear and right main gear collapsed, and the wings were bent. Density altitude was approximately 8,000 feet.