Qualification voided company's ability to negotiate (9)
I believe the answer is:
diplomacy
'ability to negotiate' is the definition.
(ability to be diplomatic)
'qualification voided company's' is the wordplay.
'qualification' becomes 'diploma' (type of academic qualification).
'voided' says to hollow out the word (remove centre letters) (void can mean to empty out).
'company' with its middle removed is 'cy'.
'diploma'+'cy'='DIPLOMACY'
(Other definitions for diplomacy that I've seen before include "Skilful handling" , "Tactful dealing" , "See 2" , "Savoir-faire" , "Art of negotiation" .)