Unreliable way of painting people unlikely to be “detailed” (13)
I believe the answer is:
temperamental
'unreliable' is the definition.
(similar in meaning)
'painting people unlikely to be detailed' is the wordplay.
'painting' becomes 'tempera' (I've seen this before).
'people' becomes 'men' (men can refer to humanity as a whole).
'unlikely' becomes 'tall' (I've seen this before).
'to be detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'tall' with its final letter removed is 'tal'.
'tempera'+'men'+'tal'='TEMPERAMENTAL'
'way of' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for temperamental that I've seen before include "Liable to mood swings" , "Liable to changes of mood" , "Given to mood changes" , "Touchy, moody" , "Erratic" .)