The answer is guarantee. Milady names the alternate term directly, in parentheses right after defining the arrangement: a salary-plus-commission (sometimes called a guarantee) compensation arrangement usually guarantees a minimum base salary plus a percentage of earnings above it.
The book notes this structure can evolve into a commission-only wage status over time, once an employee has built a loyal clientele. "Default," "percentage," and "upsell" are all plausible-sounding business terms, but none of them is the specific synonym the book gives for salary-plus-commission.
Milady Standard Barbering, 6th ed., Ch. 20 (Working Behind the Chair), p. 740: "A salary-plus-commission (sometimes called a guarantee) compensation arrangement usually guarantees a minimum base salary with a percentage of the amount over that base."
This is 1 of the real Business questions in FadeJunkie's Milady-sourced 300-question bank. See the Business practice questions page for a fuller sample, or try the Business practice quiz and flashcards for free. A one-time $15 lifetime pass unlocks the complete question bank across all 13 tested topics.
More real Business questions with sourced answers: What Should You Stress on Your Resume, What Is the Primary Concern for Barbershop Layout, What Is a Typical Job Interview Question, What Is a Guide to the Actions of an Organization, and 11 more on the Business practice questions page.
Browse every topic on the Practice Question Hub, or see the Texas Barber State Board Exam Guide for the full exam process — required hours, PSI scheduling, and fees.