When was this era?
Here is a guidebook for US army officers in 1984, https://archive.org/details/DTIC_ADA166412/page/n49/mode/2up... :
> There are certain individuals who perform services for you who should be tipped if you expect to receive good service. ... Tip a barber at least 15 percent; however, as much as 2 dollars may be appropriate in some establishments if multiple services are performed.
The Hertz Survival Manual For Traveling Businessman, 1967:
> A barber receives a 25¢ tip, and the tip for a shoeshine is 10¢.
A 1953 newspaper article on John Wayne's expenses at https://archive.org/details/sedalia-democrat-1953-05-19/page...
> Superior Judge William R. McKav commented, during the detailing of Wayne's expenses, that a star of his stature would have to tip $2 or "you and I would know what would be said"
A 1949 novel, https://archive.org/details/in.ernet.dli.2015.86579/page/n15... :
> “That does not mean that I have to look like a cheap skate,” said Seymour. “You told me to take the kid to the barber: next time take him yourself and see what happens when you don’t tip the barber.”
> “I never tip him,” said Sarah. “You’re just a big sport on your sister’s money.”
> And in fact, Sarah never tipped the barbers for the children’s haircuts and she disregarded the gestures of contempt and anger which sometimes occurred
In 1923, the result of a court case:
> On page 188 of the August issue of Office Appliances was printed an account of an experience by A. W. Morf, of the Woodstock Typewriter Company, New York, N. Y. He refused to tip a barber, and the tip was added to his check. The case came into the court of special sessions at New York, and the court fined the barber $25.00.
That's not to say everyone tipped, only that over the last century it certainly crossed the mind of quite a few people to tip the barber.