In Of Mice and Men, there is lots of evidence to suggest that the boss is not a working man. When he makes an appearance in chapter 2, for example, his physical description suggests that he does not do any physical work. He is "fat-legged," for example, and carries a time book in his pocket. These details suggest that he spends most of his time in an office and not out working the land.
In addition, we also see that the boss is not a working man through the questions he asks George. By questioning whether George is taking a cut of Lennie's pay, for example, Steinbeck makes it clear that the boss is a businessman, interested only in hard cash and profits; he is not the sort of person who works the land.
Finally, another piece of evidence comes from the previous Christmas when the boss brought a gallon of whisky to the men. The fact that he can afford so much alcohol shows that he is a businessman, not a workingman. It also shows that he enjoys the finer things in life, the sort of things that a ranch hand could never afford.