Managing store is most promising (7)
I believe the answer is:
rosiest
'most promising' is the definition.
('rosy' can be a synonym of 'promising')
'managing store is' is the wordplay.
'store is' anagrams to 'ROSIEST'.
But, I am not clear how the anagram is indicated.
Can you help me to learn more?
(Other definitions for rosiest that I've seen before include "Most optimistic - stories (anag)" , "(Of future) most promising; maximally pink" , "Most glowing" , "Most healthy" .)