For those touting the wares of the companies they represent, sometimes honesty isn't always the best policy.
But Oscar winner Helen Mirren had a moment of candour when she gave her opinion on the skincare brand by L'Oreal whose advertising campaign she fronts.
Appearing as brand ambassador at a L'Oreal panel in Cannes, she let slip her real opinion on the brand, when she said: "I'm not setting standards for others. All I can do is be who I am. I've always loved make-up.
"I'm an eternal optimist. I know that when I put my moisturiser on it probably does f--- all, but it just makes me feel better.
"I've always said to L'Oreal as well that I will only do what makes me feel better," she said in the speech reported by Campaign magazine.
Dame Helen, 72, is the face of L'Oreal's 'Age Perfect' moisturiser range, and was signed as a brand spokeswoman in 2014. She is the oldest of the brand's celebrity ambassadors and on her insistence, the advertisements she appears in are not digitally enhanced.
However comparisons were made with the speech in 1991 by Gerald Ratner who said of jewellery from the firm he founded was sold for such a low price "Because it's total crap", in a comment that wiped £500m from the company's value.
In 2002, Camelot chief executive, Dianne Thompson, let slip that players had virtually no chance of scooping the jackpot. The following year, Barclays chief executive Matt Barrett, said people should avoid the Barclaycard, because it was so expensive.
Mirren did say she had been a fan of L'Oreal products for a long time and praised it for not just using teenage models to sell its products.
A L'Oreal spokesman was not available for comment, the Telegraph reported.