Detectives are indeed very positive! (7)
I believe the answer is:
decided
'positive' is the definition.
(thesaurus)
'detectives are indeed very' is the wordplay.
I cannot really understand how this works, but
'detectives' could be 'cid' and 'cid' is located in the answer.
The remaining letters 'deed' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for decided that I've seen before include "Marked" , "Determined; resolute" , "Determined - settled" , "Categorical" , "Resolved, settled" .)