“Never sell what you haven’t got”

“Commodore” Cornelius Vanderbilt (1794-1877) was reported by at least 1870 to have said “Never sell what you haven’t got.” According to some accounts, Vanderbilt said this to fellow investor Daniel Drew; according to other accounts, Vanderbilt said this to the son of an old friend (“Sonny, never sell what you haven’t got.”).
 
“He who sells what isn’t his’n, must buy it back or go to prison” is a similar phrase from the 1800s.
     
 
Wikipedia: Cornelius Vanderbilt
Cornelius Vanderbilt (May 27, 1794 – January 4, 1877), also known by the sobriquet Commodore, was an American entrepreneur. He built his wealth in shipping and railroads and was the patriarch of the Vanderbilt family and one of the richest Americans in history.
 
Google Books
Ten Years in Wall Street;
or, Revelations of inside life and experience on change
By William Worthington Fowler
Hartford, CT: Worthington, Dustin
1870
Pg. 122:
In his extremity, he went to Vanderbilt, introduced himself as the son of his old friend, told him his situation, and asked his advice. “Never sell what you haven’t got,” grimly responded the Commodore.
 
9 December 1870, New York (NY) Herald, pg. 4, col. 4:
Further illustrations thus afforded of the soundness of the maxim—one that ought to be printed in letters of gold, and placarded conspicuously in not a few places in the city—“Never buy what you cannot pay for, and never sell what you cannot deliver.”
 
20 March 1871, New York (NY) Herald, “Financial and Commercial,” pg. 8, col. 1:
The “great American bear,” who advised the public last winter that “Wall street had two hundred millions of stocks, all for sale,” is nearly distracted at the loose and incautious manner in which the public bought the “sheers” which he offered for sale and sold before he had taken the precaution to be their owner. Doubtless he will remember
THE COMMODORE’S ADVICE,
“Sonny, never sell what you haven’t got.” 
 
Chronicling America
22 August 1871, Charleston (SC) Daily News, pg. 2, col. 1:
The maxim of the Hon. Rufus Drew, New York stock operator, is that “there are two hundred million of them ere shares in Wall street, and all for sale,” while that of Commodore Vanderbilt is, “Sonny, never sell what you haven’t got.”
         
Google Books
Men and Idioms of Wall Street:
Explaining the daily operations in stocks, bonds and gold
By John Hickling & Co
New York, NY: John Hickling & Co.
1875
Pg. 65:
Vanderbilt, also, has some maxims: 1st, never speculate; 2d, never sell what you haven’t got; 3d, hold on and wait; 4th, never tell any one what you are going to do till you have done it.
 
Google Books
The Book of Daniel Drew:
A glimpse of the Fisk-Gould-Tweed régime from the inside
By Bouck White
Garden City, NY: Doubleday, Page
1910
Pg. 177:
“After this, never sell what you haven’t got, Dannie; never sell what you haven’ t got,” was all the answer he (Vanderbilt—ed.) made. “Don’t put it in any man’s power to ruin you. By-bye.”
 
Google Books
Blessed Be Drudgery and A Cup of Cold Water
By William C. Gannett
Washington, DC: Review and Herald
1914
Pg. 20:
Who said, “The secret of a Wall Street million is common honesty”?—Vanderbilt; and he added as the recipe for a million (I know somebody would like to learn it), “Never use what is not your own, never buy what you cannot pay for, never sell what you haven’t got.”