Appeal to Celebrity

I'm not sure if I'd call this a subspecies of Appeal to Authority or a near-twin fallacy, but I'd definitely call it common as dirt.

Appeal to Celebrity
Type: Informal
Category: Red Herring (Irrelevance)
Subcategory: Genetic (Irrelevant History)

Definition
Arguing from the idea that if a well-known person affirms a proposition, the proposition is therefore true. Social status is used to falsely establish perceived reliability.

Usual Form
Statement is made that because celebrity A endorses B, B is necessarily true or of quality.

Explanation
The use of well-known and popular people as "proof" of something's value, whether brand, proposition, or person, is often thought of as a modern phenomenon, but is in fact ancient.  Celebrity endorsements of politicians dates to ancient Rome at least; ideas and philosophers have been supported by recommendation by popular figures as recorded by Plato; and the idea of leading socialites creating fads from their own whims has been joked about since the invention of satire.

Brands have even invented reliable-looking characters for their products, drawing on stereotype and accepted mores to urge consumers to trust them. Whether this is an appeal to celebrity or authority I'm uncertain. I may need to break it out into its own fallacy eventually.

The problem with appealing to celebrity recommendation is that they may not have any expertise in the area under consideration. Most famously (and hilariously), a commercial in the 80s for Vicks Formula 44 cough syrup had Chris Robinson, who played a doctor on the General Hospital soap opera, begin with his declaration, "I'm not a doctor, but I play one on TV." There are many examples of this odd, openly-false appeal to authority listed on tvtropes.org. It's become a cultural running gag.

For the most part, though, celebrity endorsements carry their influence by simple weight of whatever made them a celebrity in the first place. Sure, a basketball star is a natural choice for promoting athletic shoes because he has extensive experience with them; but Michael Jordan has endorsed not only Nike but also Rayovac batteries, Hanes underwear, and Ball Park Franks. There is precious little to explain why an actor's political views should be taken as guidance, or what coffee a baseball player prefers should make any difference to the sports fans. The song Space Oddity pokes at this when Ground Control tells the astronaut that "the papers want to know whose shirts you wear."

The fact is, there is an assumption that popularity is built on something real and valuable. It's more or less part of the social fact of humanity, and a way to shorten the path to assurance that a belief about something can be relied upon. The assumption runs so deeply that it is not only unquestioned but unnoticed a lot of the time. As a result, it can be manipulated as a conscious or unconscious strategy by everyone from major marketers to high school cliques.

Then there's the problem that a celebrity being paid to voice an opinion calls into question the veracity of their claim. Honestly, in what other area is openly paid opinion considered valid?

Examples
"Oprah says we shouldn't eat after 6pm. It's not healthy."
Oprah is not a dietician. Moreover, she has changed her views on such things wildly over the course of her career, based on changing which dietician she is following at the moment.

George Clooney endorses a coffee machine, a whiskey, and more. Would I like to be like George? Heck yeah!
Will drinking Nespresso make me more like George? Not a whit. Given his personal opinion rather than paid endorsement, however, I'd say that a man with approximately unlimited options would choose the best item that fits his tastes.