In April 1927, Wagner was the key prosecution witness in the trials of actors Paul Kelly and Dorothy Mackaye. Wagner was Kelly's roommate and was present when Kelly beat to death Mackaye's husband, Ray Raymond, at an alcohol-fueled party on April 16. Kelly served two years in prison on a manslaughter conviction. Mackaye was sentenced to 10 months on an accessory conviction.
Max Wagner, who was raised in Mexico, was an accomplished piano player and often composed and sang Mexican folk ballads. One of his arrangements, "Pedro Rudarte y Simon," appeared in "The Last Trail" (1933).
The United Press reported on the set of The Mad Doctor, also titled A Date with Destiny (1941), that Wagner "traveled" 50,000 miles as an on-screen taxi driver during his acting career. "I was cast as a taxi driver about five years ago," Wagner told a reporter. "And was typed.".