To make a mess is a bewildering thing to do (7)
I believe the answer is:
confuse
'to make a mess' is the definition.
I can't judge whether this definition defines the answer.
'bewildering thing to do' is the wordplay.
'bewildering thing' becomes 'fuse' (I can't explain this - if you can you should give a lot more credence to this answer).
'to' means one lot of letters go next to another (I've seen this in other clues).
'do' becomes 'con' (both can mean to defraud).
'fuse' after 'con' is 'CONFUSE'.
'is a' is the link.
Can you help me to learn more?
(Other definitions for confuse that I've seen before include "Perplex" , "Muddle, mix up" , "Puzzle" , "Bewilder" , "Disconcert, befuddle" .)