Final answer:
Barney Northrup's effectiveness as a salesman can be likened to that of historical figures like Andrew Carnegie, who displayed exceptional salesmanship by expanding his business and maintaining profits.
Step-by-step explanation:
The proof that Barney Northrup was a good salesman can be inferred from various examples of proficient salesmen throughout history. One such individual was Andrew Carnegie, who, despite not being a scientific expert in steel, excelled as a promoter and salesman - securing financial backing and making shrewd business decisions to expand his enterprise. Carnegie capitalized on smart business moves, saved profits during good times, and purchased other companies at low prices during recessions. Similarly, the value of a good salesman can be measured by their ability to handle miscommunication and maintain a national reputation for their products and services, a major asset for any company.