Oxford operates a janitorial service and cleans commercial buildings. Oxford contracted with Gresham to clean several buildings on a regular basis, not knowing that Gresham was only an agent hired to manage these buildings. Gresham failed to make several payments owed to Oxford. When Oxford sued Gresham for the money owed, Gresham argued that he was not liable since he was merely an agent. Is Gresham correct? Why or why not?