Never get involved in a land war in Asia.
That's the most famous piece of advice, but only slightly less well-known is this: Never go against a Sicilian when death is on the line!
The only advice I have that hasn't been mentioned already, would be to come up with a list of a few good websites, forums, books, etc. to help point people in the right direction when you recommend researching their fish.
*EDIT* Doh! It appears I'm the head of the department or redundancy department which I am the head of...