Tries purchasing top of trouser suit (6)
I believe the answer is:
hearts
'suit' is the definition.
(hearts is a playing card suit)
'tries purchasing top of trouser' is the wordplay.
'tries' becomes 'hears' (as in trying or hearing in a trial).
'purchasing' indicates putting letters inside (some letters take possession of others).
'top of' suggests taking the first letters.
The initial letter of 'trouser' is 't'.
'hears' enclosing 't' is 'HEARTS'.
(Other definitions for hearts that I've seen before include "Card game and centres of emotions, it's said" , "Cores" , "Vital organs in the pack" , "Suit in pack" , "Card suit and essential organs" .)