Act of taking over commercial selection? (8)
I believe the answer is:
adoption
'act of taking over' is the definition.
(to adopt is to take over or take on)
'commercial selection?' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'selection?' becomes 'option' (both can mean a choice).
'ad'+'option'='ADOPTION'
(Other definitions for adoption that I've seen before include "Choosing (of a candidate for office)" , "fostered" , "Legal process of taking a child into one's family" , "formal selection of candidate?" , "Appropriation from another source" .)