Charm stubborn person into returning thanks (6)
I believe the answer is:
amulet
'charm' is the definition.
(I know that amulet is a type of charm)
'stubborn person into returning thanks' is the wordplay.
'stubborn person' becomes 'mule' (I've seen this in another clue).
'into' indicates putting letters inside.
'returning' shows that the letters should be reversed in order.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'ta' in reverse letter order is 'at'.
'mule' going within 'at' is 'AMULET'.
(Other definitions for amulet that I've seen before include "Charm protecting against evil" , "Charm worn against bad luck" , "Charm to protect from evil" , "that's charming" , "Protective charm" .)