Prying scoundrel promises to pay (7)
I believe the answer is:
curious
'prying' is the definition.
('curious' can be similar in meaning to 'prying')
'scoundrel promises to pay' is the wordplay.
'scoundrel' becomes 'cur' (I've seen this before).
'promises to pay' becomes 'ious' (more than one iou).
'cur'+'ious'='CURIOUS'
(Other definitions for curious that I've seen before include "Eager to learn, strange" , "Unusual; eager to learn" , "Eager to know something, perhaps nosy" , "Strange - inquisitive" , "Odd or eager to know" .)