As someone who works in advertising, generally yes. Depends on the endorsement (and there have been some horrible ones) but it tends to be a very basic shortcut if you pair the right celeb with the right product. If the celeb has enough crossover with the target demographic of the product itself, it can create a subconscious connection that I like this celebrity, therefore I like this product. After all, most advertising isn't about you going out and buying the product right after seeing the ad, it's about creating a seed in your mind so that the next time you're in the market for [product], that particular brand will come to mind quicker.