The pilot-in-command and pilot/passenger, a prospective buyer of the tailwheel equipped Piper PA-22-108, departed on a test flight. During the pilot/passenger's first landing, and approximately 75-100 feet into the landing roll, the aircraft began to veer to the right departing the right side of runway 31 and eventually impacting a barbed wire fence. The pilot-in-command reported no mechanical difficulties with the aircraft and light and variable winds at the time.