This author will say almost everybody is wrong (7)
I believe the answer is:
illegal
'is wrong' is the definition.
(I've seen this before)
'this author will say almost everybody' is the wordplay.
'this author will' becomes 'ill' (I can't justify this - if you can you should believe this answer much more).
'say' becomes 'eg' (both can mean for example).
'almost' means to remove the last letter (almost the whole word is kept).
'everybody' becomes 'all' (all people).
'all' with its final letter taken away is 'al'.
'ill'+'eg'+'al'='ILLEGAL'
Can you help me to learn more?
(Other definitions for illegal that I've seen before include "Contrary to law" , "murder sure is!" , "Black" , "Felonious" , "Ignoring certain acts" .)