He lives by his wits taking top people back (4)
I believe the answer is:
spiv
'he lives by his' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'wits taking top people back' is the wordplay.
'wits' becomes 'vis' (I can't explain this - if you can you should believe this answer much more).
'taking' is an insertion indicator.
'top' suggests taking the first letters (in a down clue, the first letter is top).
'back' says the letters should be written backwards.
The initial letter of 'people' is 'p'.
'vis' placed around 'p' is 'vips'.
'vips' written backwards gives 'SPIV'.
Can you help me to learn more?
(Other definitions for spiv that I've seen before include "Disreputable dealer" , "Flash fellow" , "Unscrupulous dealer" , "Flashily dressed dodgy dealer" , "Shady dealer" .)