I wouldn't call this a manual for "fanatical" customer support, though.
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Never rush to solve a problem - the problem may solve itself
In most cases it is something the user did wrong at their end.
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Give them some homework
Ask them to perform an action. There is nothing more off-putting than homework.
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Mention there may be cost involved
Check if it's not something at your end. Explain to the customer that it's likely to be something at their end. It's not worth your time if it's not worth their money.
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I'm afraid you just have to go and do it ...
Never reply with a solution - only reply with a link to a solution in your knowledge base. You may have add one first if none exists.
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Follow-up on your reply before closing the issue
Find out what the root cause was and either add an entry to the knowledge base or upvote an existing entry