Self-praise is no recommendation

self-praise is no recommendation (at all)

1. Praise of oneself is worth nothing, as one cannot be objective of one's own work or accomplishments. So many companies claim to be the best in the business at this or that in their marketing, but self-praise is no recommendation, so I can never take them seriously. A: "This is the best work we've ever done. People are going to absolutely go crazy for it!" B: "Self-praise is no recommendation at all, Jim. We'll have to wait and see how it does on the market."
2. Praising oneself reveals one's arrogance or selfishness, which in turn lowers other's opinion of one. He's constantly bragging about how much money he makes and how important his job is, but he doesn't have any friends because no one can stand to be around him! Self-praise is no recommendation, after all. A: "Would you agree that you're one of the best musicians in the world right now?" B: "Self-praise is no recommendation at all, so I don't think it would be very seemly of me to answer that."
See also: no, recommendation
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

Self-praise is no recommendation.

Prov. If you praise yourself, people will think that you are boastful and will not respect you. After listening to the lawyer brag about his achievements for a solid half hour, I decided I would find someone else to handle my case. Self-praise is no recommendation.
See also: no, recommendation
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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References in classic literature ?
'Sophronia, darling, Mr and Mrs Boffin will remind you of the old adage, that self-praise is no recommendation.'
WITH regards to Operation Furan by South Wales Police (Echo, September 30) it would appear that Chief Superintendent Josh Jones has not heard that self-praise is no recommendation.
I KNOW self-praise is no recommendation...but I'm thrilled to see other newspapers now regularly call Lord Woolf the "Lord Chief Injustice".
I have known a number of heroes in my time who believed in the saying, 'self-praise is no recommendation'.