There are all types in his trade (7)
I believe the answer is:
printer
'there are all types in his trade' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'in his trade' is the wordplay.
I cannot quite see how this works, but
'in' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for printer that I've seen before include "Compositor" , "Computer attachment to produce paper documents" , "Producer of reading material" , "Computer peripheral" , "one making an impression?" .)