Below are some quotes to give a different perspective on expertise.

I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.
Richard Feynman
US educator & physicist (1918 – 1988)
http://www.quotationspage.com/quote/799.html

There’s a sucker born every minute.
P.T. Barnum
http://en.thinkexist.com/quotes/p.t._barnum/

You can fool all the people some of the time, and some of the people all the time, but you cannot fool all the people all the time.
Abraham Lincoln
http://www.brainyquote.com/quotes/quotes/a/abrahamlin110340.html

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So let’s agree that a con artist is not an expert but others might not be able to tell the difference, at least not straight away.

More seriously, you might also consider experts by contrasting them to novices.
http://newton.nap.edu/html/howpeople1/ch2.html
So in this way you can distinguish what it means to be expert, on the one hand, from what it means to be regarded as expert, on the other.