Celebrities are role models for some, gods for other and just people for remaining. What celebrities endorse becomes the talk of the town, there are posters here and there of every new promotions by the celebs. What endorsing here implies is promotion and promotion implies expanding the publicity of something good and if that 'good' backfires, I will make the celeb responsible.
Promotion should be done only when the quality of the product is checked and assured as several people and not just one person is affected by such endorsement.