If you’re old enough to remember the days when freak shows were in carnivals and not daytime television, you may know about the barker and the shill.  These were carnival employees who both worked to entice customers into entering the mysterious realm of the sideshow, only, their methods were very different.  The barker - the correct terminology is the “talker” - was a P.T. Barnum-like character, a bold salesman who sang the praises of the exhibits.  Although he was given to the hyperbole of marketing, he made no bones about his agenda: He wanted your business.

The shill was a very different animal.  His job was to stand amidst the crowd and pose as one of their number; he would then feign awe as he claimed to have seen the show and that it was truly a jaw-dropping experience.  He was trading on his illusion of impartiality, knowing it lent him a capacity to convince that eluded the talker with his obvious agenda.....

Selwyn Duke - http://www.americanthinker.com/2007/01/the_barker_and_the_shill_the_f.html