“People buy from people they like” is a sales axiom; other things being roughly equal (such as price and quality), people make purchases from someone they like. Dale Carnegie’s popular self-help book, How To Win Friends and Influence People (1936), has a section titled “Six Ways to Make People Like You.”
 
People “buy from people they like” has been cited in print since at least 1920 and “People like to buy from people they like” was used in 1946. The saying was popular in automobile advertisements from the 1950s-1970s and in the software industry in the 1990s.
 
   
Wikipedia: How to Win Friends and Influence People
How to Win Friends and Influence People is one of the first bestselling self-help books ever published. Written by Dale Carnegie and first published in 1936, it has sold 15 million copies world-wide.
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Six Ways to Make People Like You
1.Become genuinely interested in other people.
2.Smile.
3.Remember that a person’s name is, to that person, the sweetest and most important sound in any language.
4.Be a good listener. Encourage others to talk about themselves.
5.Talk in terms of the other person’s interest.
6.Make the other person feel important – and do it sincerely.
 
Google Books
29 December 1920, The Jewelers’ Circular, pg. 112, col. 2:
The Art of Making Customers Like You
Written Expressly for The Jewlers’ Circular
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Some purchasers pay closer attention to quality and price than others do. Some buyers think more of the dollars and cents involved than of the personality of the seller. But there are those who go to the other extreme and buy from people they like, almost regardless of competitor’s values.
 
So it is plain enough that it is going to pay well to make purchasers like you. To be a friend of a prospective buyer does give you an advantage you cannot aford to discard, even though you do know yours is the best line of goods and the best store in the city.
 
Google Books
How to Select Better Salesmen
By William Rados
Prentice-Hall, inc.
1946
Pg. 362:
Enemies. Do you enjoy buying anything from a sourpuss? Neither does your trade. People like to buy from people they like.
 
18 February 1959, Albuquerque (NM) Tribune, Auto Show Section, pg. 20, col. 1:
But he really cornered the tire business by exercising a principal he has long felt to be true. “It’s pretty well known that people buy from people they like. That goes from haircuts to automobiles and there isn’t any amount of high pressure advertising that will ever change it,” he said.
(Frank Grosbeeck Jr. of Galles-Groesbeeck Motor Co.—ed.)
     
Google News Archive
28 February 1964, Washington (PA) Reporter, pg. 13, col. 1 ad:
We aim to please because people tend to buy from people they like!
(George Stewart Motor Company—ed.)
 
15 October 1972, Danville (VA) Register, pg. 11D, col.  ad:
PEOPLE BUY FROM PEOPLE THEY LIKE!
(Danville Chrysler-Plymouth—ed.)
     
Google Books
People, Power, and Organization:
A guide to using OrgAnalysis for individual and organization development
By Daniel A. Tagliere
New York, NY: AMACOM
1973
Pg. 203:
People tend to buy from people they like, and one of the most pleasant relationships is between friends.
 
Google Books
Solving Business Problems with MRP II
By Alan D. Luber
Bedford, MA: Digital Press
1991
Pg. 286:
There is an old saying in the software industry: “People buy from people they like.”
 
Google Books
Soft Sell:
The new art of selling, self-empowerment, and persuasion
By Tim Connor
Naperville, IL: Sourcebooks Inc.
1994
Pg. 78:
Here’s an old sales axiom: “Other things being equal, people buy from people they like.”
   
Google Books
Selling with Integrity:
Reinventing sales through collaboration, respect, and serving
By Sharon Drew Morgen
San Francisco, CA: Berrett-Koehler Publishers
1997
Pg. 26:
People only buy from people they like. Dale Carnegie taught us that sixty years ago. He just taught the behaviors around making people like you as a task without addressing the beliefs or skills that make relationship possible.
 
Realty Times
Published: September 28, 2000
Who Says You Shouldn’t Talk About Yourself On Your Web Site?
by Lawrence Schoeffler
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Have we undergone some massive cultural shift when I wasn’t looking? I thought people wanted to know who they’re doing business with. I thought the old sales axiom: “People buy from people they like,” was immutable. All of a sudden people buy from people they don’t know anything about? My head is spinning.
     
WebProNews
Why You’re Not Blogging - And Why You Should Start Today
Tinu Abayomi-Paul
Expert Author
Published: 2005-04-20
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People buy from people they like. I don’t remember who said it first, but I’ve learned that it’s the truth.
 
Google Books
People Buy You: The Real Secret to What Matters Most in Business
By Jeb Blount
Hoboken, NJ: John Wiley
2010
Pg. ?:
Myth #2: People Buy from People They Like
   
Street Corner (Eastern Suburbs, Sydney)
20 Ways To Improve Your Small Business Marketing
by Mellissah
22/04/2010
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2. Be passionate about what you do – the old saying ‘people buy from people they like’ is on the money. Let your customers and clients know you enjoy what you do.
   
Google Books
Brand It Like Barack!:
How Barack Obama Sold Himself to America and what You Can Learn from This
By Gary Kaskowitz
Indianapolis, IN: Dog Ear Publishing
2010
Pg. 98:
People buy from people they like. People buy from people like them. These are axioms in sales and copywriting that hold true for politics.