He may prophesy that the vendor will lose fifty quid (4)
I believe the answer is:
seer
'he may prophesy that the vendor will lose fifty quid' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'see' and 'see' is found within the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for seer that I've seen before include "Oracle or prophet" , "Wise person" , "One has unusual foresight" , "wise fellow" , "Fortune-teller" .)