Work on sales pitch, overlooking one truthful message? (6)
I believe the answer is:
gospel
'truthful message?' is the definition.
(as in the Christian gospels)
'work on sales pitch overlooking one' is the wordplay.
'work on' becomes 'go' (synonyms. I am not sure about the 'on' bit.).
'sales pitch' becomes 'spiel' (I've seen this before).
'overlooking' suggests deleting specific letters.
'one' becomes 'I' (Roman numeral).
'spiel' with 'i' removed is 'spel'.
'go'+'spel'='GOSPEL'
(Other definitions for gospel that I've seen before include "Truth (religious)" , "Holy book" , "church music" , "Mark, perhaps" , "Unquestionable truth - church doctrine" .)