Pedro Carvalho, founder of PR company FNIK, was commenting on the behaviour of Jade Goody in Celebrity Big Brother.
He said: "Celebrities should have to undergo some sort of training before they are allowed to represent a charity. If they are committed to the cause, they will do it. If not, the charity shouldn't take them on."
Carvalho said Celebrity Big Brother should serve as a warning to charities.
"I don't see how any charity could justify working with Jade Goody again after this," he said. "Anyone who does so should be ashamed."
Louise Burfitt-Dons, founder of charity Act Against Bullying, said that celebrity training was a good idea in theory, but would not be a guarantee against bad publicity. "There is still the chance you will be associated with a celebrity who has not been vetted if they buy a ticket to one of your events and are photographed there," she said.