The American-English phrase would you buy a used, or a second-hand, car from this man? was originally used during the 1960 presidential election campaign by the Democratic Party to denigrate the incumbent Vice President Richard Milhous Nixon (1913-1994), who was the Republican Party’s presidential nominee.

The earliest occurrence of the phrase that I have found is from the account by Arthur Edson, of the Associated Press, of the party that the Democratic Party threw on Sunday 10^th July 1960 at the Beverly Hilton hotel of Los Angeles, California, the day before the Democratic National Convention opened—account published in several U.S. newspapers on Monday 11^th July 1960, for example in The Cedar Rapids Gazette (Cedar Rapids, Iowa):

The Democrats, the story runs, will buy 20-second TV spots in which the picture of Vice-president Nixon is flashed on the screen.
While the viewer watches the picture, the announcer is supposed to intone: “Would you buy a used car from this man?”

The second-earliest occurrence of the phrase that I have found is from the account by A. A. Michelson of the Democratic National Convention, published in The Berkshire Eagle (Pittsfield, Massachusetts) of Thursday 14^th July 1960:

Some members of the California delegation, preoccupied at the beginning of the week with the battle to win that state’s allegiance for Kennedy ¹, have now put their heads together to map out some post-convention campaign strategy. One suggestion: a televised photograph of Vice President Nixon, captioned—“Would you buy a second-hand car from a man like this?”

¹ The Democratic statesman John Fitzgerald Kennedy (1917-1963) was the 35^th President of the USA from 1961 until his death.

The phrase then occurs in an article about Richard Nixon by J. A. Dear, published in The Sedalia Democrat (Sedalia, Missouri) of Thursday 28^th July 1960—the National Convention of the Republican Party was held in Chicago, Illinois, from 25^th to 28^th July 1960:

Tonight he [= Richard Nixon] swings into the final lap as his party’s candidate for the Presidency.
Of course he’s had luck. But it took more than luck to get him this far along the road.
And in a sense he’s been unlucky. For his rise has depended on enduring a succession of degrading and humiliating experiences.
People have thrown rocks at him. People have spit at him. Many of his fellow Americans ask with a chuckle: “Would you buy a second hand car from this guy?”

This portrait of Richard Nixon was published in The Sedalia Democrat (Sedalia, Missouri) of Thursday 28^th July 1960:

In his column published in The Jackson Sun (Jackson, Tennessee) of Thursday 3^rd January 1963, Walter Winchell (1897-1972) wrote that the phrase was applied to an unspecified mayor:

On the wall of a newspaper office: A photo of the Mayor captioned: “Would You Buy a Used Car from This Man?”

According to the U.S. cartoonist and humorist Al Capp (Alfred Gerald Caplin – 1909-1979) in the only “lecture”, entitled Political Satire, that he delivered at Hickory Hill ², the person who coined the phrase about Richard Nixon remained anonymous—this is the relevant passage from the “lecture”, as published in the Wilmington Morning News (Wilmington, Delaware) of Saturday 13^th April 1963:

“[One of the “modern satirists [who] provably affected the course of American life”] was the author of the line that was supposed to have appeared under a life-sized, smiling photograph of Richard Nixon—“Would you buy a used car from this man?” That provoked enough voters into thinking about the real issue of the ’60 campaign to elect Kennedy.
“Although the author of that one line had a greater effect on the course of American life than all the Kennedy speech writers, he has never stepped forward and claimed the credit and the ambassadorship to which he was so richly entitled”

² Robert Francis Kennedy (1925-1968), John Fitzgerald Kennedy’s brother, organised regular “seminars” at Hickory Hill, his house in McLean, Virginia.

Walter Winchell wrote the following in his column, published in the Lebanon Daily News (Lebanon, Pennsylvania) of Tuesday 1^st October 1963:

The Repubs have finally come up with a snappy retort to the Demo’s 1960 insult: “Would you buy a used car from Nixon?” . . . They will quip: “Would you lend Kennedy your PT boat ³?”

³ The term PT boat (short for Patrol Torpedo boat) designates a motor torpedo boat used by the military. In 1943, the PT boat commanded by John F. Kennedy came into collision with a Japanese destroyer.

Interestingly, the Republican Party used the phrase to denigrate the incumbent Democratic President Lyndon Baines Johnson (1908-1973) during the 1964 presidential campaign—as explained, for example, by the Detroit Daily Press (Detroit, Michigan) of Friday 9^th October 1964, which states that the phrase is hackneyed:

Sen. Barry Goldwater ⁴ and his strategists believe they have found the so-called gut issue of the presidential campaign.
The issue is President’s Johnson’s image, and the Goldwater strategy board feels it comes down to the time-worn political jibe: Would you buy a used car from him?
Ironically, this line is the same one the Democrats used against the last GOP presidential nominee, Richard Nixon, in 1960.

⁴ Barry Morris Goldwater (1909-1998) was the Republican Party’s presidential nominee in 1964.

Likewise, on Tuesday 20^th October 1964, The Province (Vancouver, British Columbia) mentioned:

a Goldwater’s slogan: “Would you buy a second-hand car from Lyndon Johnson?”