“If something sounds too good to be true, it probably is”

“If it sounds too good to be true, it usually is” was a catchphrase used by the Better Business Bureau to alert the public to shady business practices. The phrase was used since at least 1954; in 1962, the BBB produced a short film titled Too Good To Be True.
 
The first half of the phrase varies with “If it sounds too good to be true” or “If it looks too good to be true” or “If it seems to good to be true.” The second half of the phrase varies with “it usually is” or “it probably is” or simply “it is.” 
 
The phrase “too good to be true” was applied in 2008 to Bernard Madoff, who was accused of running a $50 billion Ponzi scheme. Members of the investment community concluded that Madoff’s “too good to be true” investment returns should have raised red flags.
   
 
The Free Dictionary
too good to be true
not to be believed or likely to be real
They told me I’d be going on business trips to Europe, but it sounded too good to be true.
See also: good, true
Cambridge Dictionary of American Idioms Copyright © Cambridge University Press 2006.
       
(Oxford English Dictionary)
Proverbial phr. too good to be true.
[1578 G. WHETSTONE Promos & Cassandra B3, I thought thy talke was too sweete to be true.]
1580 T. LUPTON (title) Siuquila. Too good to be true.
1594 J. LYLY Mother Bombie IV. ii, in Wks. (1902) III. 208 It was too good to be true.
a1691 J. FLAVEL Method of Grace (1699) vii. 133 They thought it was too good to be true.
1849 GEO. ELIOT Let. May (1954) I. 282 There is a sort of blasphemy in that proverbial phrase ‘too good to be true’.
   
Wikipedia: Better Business Bureau
The Better Business Bureau (BBB), founded in 1912, is not a government agency, but a private business franchise of local BBB organizations based in the United States and Canada, which work together through the Council of Better Business Bureaus (CBBB). The BBB goal is to foster a fair and effective marketplace, so that buyers and sellers can trust each other (“Start With Trust”). Many BBB services can be accessed online through their website.
 
BBBs gather and report information on business reliability, alert the public to frauds against consumers and businesses, provide information on ethical business practices, and act as mutually trusted intermediaries between consumers and businesses to resolve disputes. News media frequently turn to the CBBB and local BBBs as expert sources of news about scams and consumer issues.
 
5 December 1954, Oakland (CA) Tribune, “Don’t Be a Sucker for Christmas Swindlers” by Victor H. Hyborg as told to Lester David, Parade magazine, pg. 3, col. 4:
THE AUTHOR: Victor H. Nyborg is president of the Association of Better Business Bureaus, which guards against shady business practices in the U.S. and Canada.
(...)
Remember if a bargain seems too good to be true, it usually is.
     
Google Books
Dress well on $1 a day
By Bea Danville
Published by W. Funk
1956
Pg. 185:
Once again, we quote the Better Business Bureau: “If it sounds too good to be true, it usually is.”
 
Google News Archive
27 April 1961, St. Petersburg (FL) Times, “‘Offer’ Probably Is Too Good To Be True” by Sylvia Porter, pg. 2D, col. 4:
So perhaps the most valuable of all the guides I could suggest in this closing sentence of this series is: If any deal or offer seems too good to be true, beware, for it almost always is.
   
BFI Film & TV Database
TOO GOOD TO BE TRUE
(1962)
Sponsor: Association of Better Business Bureau
   
12 May 1963, New York (NY) Times, “Around the Garden” by Joan Lee Faust, pg. X22:
There never are any bargains in plants. As the Better Business Bureau states: “Remember the offer that seems too good to be true usually is.”
   
Google Books
The Balance sheet
Published by South-Western Pub. Co., 1964
Item notes: v. 46
Pg. 37:
Too Good to Be True. 1962. This is a 16mm, sound motion picture in color produced by Audio Productions and presented by the Association of better Business Bureaus, Inc. This 20-minute film, moderated by TV personality Bud Collyer, is highly informative about alluring but insincere advertising practices known as “bait and switch.”
 
22 July 1965, New York (NY) Times, “If Price Seems Too Good to Be True, It May Not Be” by Sal Nuccio, pg. 45:
When a product or service is offered at a price that seems too good to be true, there is a good chance that it isn’t.
   
The bargain-price offers that are real are those of reputable sales organiations that periodically offer sales. Some of them occasionally will offer an item at an especially low price—perhaps below cost—in the hope of luring customers into their stores, where they may buy other merchandise at regular prices.
 
However, according to the Metropolitan Better Business Bureau, consumers also have been pounded with barrage after barrage of dishonest offers by a number of unethical promoters.
 
4 July 1966, New York (NY) Times, “Personal Finance” by Sal Nuccio, pg. 24, col. 2:
Rather than risk being trapped, the person considering a product offer—any product offer—that appears too good to be true should check on the company making the offer. He may do that at this local Better Business Bureau or a regulatory agency, which in New York may be the Consumer Frauds and protection Bureau of the State Attorney General’s office.
 
9 October 1967, New York (NY) Times, pg. 17 ad:
A&S suggests that you join the wise shoppers who check The Better Business Bureau when they are in doubt about solicitations or business offers that are too good to be true!
(Abraham & Straus stores—ed.)
   
Google Books
Good Housekeeping
Published by Hearst Corp., 1968
Item notes: v. 167
Pg. 40:
One rule of thumb is to avoid anything that sounds too good to be true. It probably is exactly that!
     
Google Books
Consumer Swindlers and How to Avoid Them
By John L. Springer
Published by H. Regnery Co.
1970
Pg. 189:
ONE OF the most common remarks found in literature produced by Better Business Bureaus is the statement: “If an item for sale sounds too good to be true, it probably is.”
 
Google News Archive
24 April 1970, Spokesman-Review (SPokane, WA), pg. 1, col. 8:
Here a bit of wisdom that la said to have prevented many a swindle: If it sounds too good to be true…it probably is!
   
26 February 1976, New York (NY) Times, “23% of U.S. Mail Frauds Originate in Local Area” by Will Lissner, pg. 33:
So the New York Post Office marked Postal Consumer Protection Week atthe General Post Office at Eighth Avenue and 33d Street yesterday, and opened a campaign to warn the public to “beware” and to heed the adage, “If it sounds too good to be true, it probably is….”
 
Google News Archive
20 July 1976, St. Petersburg (FL) Times, pg. 8A, col. 1:
It would be unfair to dismiss these time-sharing or right-to-use schemes sweeping the real estate scene simply by invoking the old consumer protectionist cliche, “If it sounds too good to be true, it probably is too good to be true.” 
       
10 September 1977, New York (NY) Times, “Consumer Notes” by Alfonso A. Narvaez, pg. 55:
Watch out for the bargain that sounds just too good to be true—it probably isn’t.
 
27 November 1979, New York (NY) Times, “Taxes” by Deborah Rankin, pg. D2:
Tax experts warn that if a year-end shelter sounds too good to be true, it probably is.
   
OCLC WorldCat record
If it sounds too good to be true ... it probably is!
Author: Ohio. Attorney General’s Office.
Publisher: Columbus, Ohio : Attorney General’s Office, [1981]
Edition/Format: Book : State or province government publication : English
 
New York (NY) Post
MADOFF’S STRATEGY WAS JUST TOO GOOD TO BE TRUE
By MARK DeCAMBRE
December 13, 2008
Though it may take some time to understand the scope of the massive scam that Bernard Madoff is accused of pulling off, it’s becoming clear that the investment strategy he touted couldn’t on its own produce the results he boasted about.
 
Observers say that Madoff’s investment strategy alone would have suffered massive losses during the current stock market rout, had it not been helped along by what Madoff himself described as a Ponzi scheme.
   
Bloomberg.com
Investment Adviser Aksia Warned Clients of Madoff ‘Red Flags’
By David Glovin, Karen Freifeld and David Voreacos
Dec. 13, 2008 (Bloomberg)
(...)
Aksia’s Jim Vos said he spent several months probing Madoff’s firm on behalf of clients, only to recommend against investing in it. Vos, who had an investigator stake out the New City office, said eight “feeder funds” invested about $15 billion with Madoff. Vos declined to name the clients.
 
“I’m shocked by how investors turned a blind eye to returns that were too good to be true, constant steady small positive monthly returns,” Vos said. “When something is too good to be true, it probably is.”