Throw in a diamond as sales talk (5)
I believe the answer is:
pitch
This might be a double definition.
'throw in a diamond' is the first definition.
'pitch' can be an answer for 'throw' (pitch is a kind of throw). I am not sure about the 'in a diamond' bit.
'sales talk' is the second definition.
(synonyms)
'as' acts as a link.
Can you help me to learn more?
(Other definitions for pitch that I've seen before include "To throw; roof slope" , "-- and putt" , "Scene of game (don't touch it!)" , "Distillation of tars" , "Tone - football field" .)