Appeal to authority
The appeal to, or argument from, authority fallacy is one of the most misused fallacies in our (admittedly limited) experience. As skeptics we like to support our arguments with data, statistics, studies or, often, just quoting respected and knowledgeable individuals or institutions. On many occasions this is dismissed as an appeal to authority, allowing our interlocutor to waive away almost any supporting evidence we can bring. Even the great Carl Sagan wrote: 'One of the great commandments of science is, "Mistrust arguments from authority"...Too many such arguments have proved too painfully wrong. Authorities must prove their contentions like everybody else.'
But there is a fundamental misunderstanding at the heart of this fallacy, it is not wrong to use an authority on a subject when the authority has the support of the evidence and has demonstrated this in its actions, the error is in mixing real authorities with those that aren't relevant to support your argument. For example, If 1000 scientists who study climate say the planet is warming because of human activity, then it would be fallacious to dismiss these claims because someone who was once in charge of the UK economy (no matter how well versed in economics) says its not. On the flip side of this, there must always be room for authorities - however knowledgeable - to be wrong.
It often comes down to trusting experts and it is easy to dismiss them as being narrow-minded and too wrapped up in academia to understand the 'real-world'. But experts are labelled as such because they have built up their expertise over time and using the tools of science - peer review, evidence gathering, experimentation, journal entries, conferences etc - they have done the donkey work in their subject. It is always wise to have a healthy scepticism of claimed expertise, it is not enough to simply assert their authority; they need to have demonstrated it and when they have done so, then they can be called in to support your argument. It is also very important to remember that when they stray outside of their subject they are just as likely to be wrong as the rest of us. Lets not dismiss experts though, it is through their efforts that human knowledge advances and is continually refined.