Standards one’s needed to seal business arrangement (6)
I believe the answer is:
ideals
'standards' is the definition.
(I have seen 'High standards ' mean 'ideals' so perhaps 'standards' could also mean 'ideals')
'one's needed to seal business arrangement' is the wordplay.
'one's' becomes 'I's' (Roman numeral).
'needed to seal' indicates putting letters inside (inserted letters are sealed in).
'business arrangement' becomes 'deal' (eg a deal between two businesses).
'is' enclosing 'deal' is 'IDEALS'.
(Other definitions for ideals that I've seen before include "Ladies (anag.)" , "High values for ladies" , "High standards for ladies" , "'Perfect models, highest notions (6)'" , "They're perfect" .)