The problem with celebrity endorsements is twofold. First, companies can mask their own dubious propositions by letting a popular, trusted personality do the dirty work for them.

The other issue is that reputable companies can't control their celebrity mouthpieces outside the soundstage. Tiger Woods' infidelity was a disaster for all involved with his "brand." Regardless of final legal dispositions, sports heroes Ben Roethlisberger and Kobe Bryant were still accused rapists, bad news for those banking on them at the time of allegations.
Pushing debit cards, gold coins and fried, fatty foods (as does Paula Deen, a recently revealed diabetic) is how some celebrities pay the bills.

When it comes to commercials and endorsements, not all celebrities are created equal.

A study released last year by advertising analysts at Ace Metrix, Celebrity Advertisements: Exposing a Myth of Advertising Effectiveness, tested more than 2,600 television ads over the course of 2010 and found less than 12% of ads using celebrities "exceeded a 10% lift versus average industry norms" -- in other words, benefited from the association -- and nearly 20% of celebrity ads yielded "negative lift scores."

"This research proves unequivocally that, contrary to popular belief, the investment in a celebrity in TV advertising is very rarely worthwhile," CEO Peter Daboll said.

The underperforming celebrities that year included Tiger Woods (23% less effective than average), Lance Armstrong, Kenny Mayne, Dale Earnhardt Jr. and Donald Trump. Celebrities who created the most "life" included, as one might expect, Oprah Winfrey and, more surprising, filmmaker Ed Burns and former Rocky nemesis Carl Weathers.

Despite those findings, companies still flock to celebrities to help put a shine on their products and services, and the famous are often quite mercenary in their approach -- willing to risk reputation if the price is right.

Here are 10 examples of celebrity endorsements that raised eyebrows, if not came across as flat-out sleazy.

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