Source of better advice upset rest somehow (7)

I believe the answer is:
tipster
'source of better advice' is the definition.
'tipster' can be an answer for 'source' (thesaurus). I am unsure of the 'of better advice' bit.
'upset rest somehow' is the wordplay.
'upset' becomes 'tip' (I've seen this in another clue).
'somehow' indicates anagramming the letters.
'rest' with letters rearranged gives 'ster'.
'tip'+'ster'='TIPSTER'
Can you help me to learn more?
(Other definitions for tipster that I've seen before include "better counsellor" , "Race winner forecaster" , "Betting pundit" , "One predicting winners" , "One giving better advice" .)
