Sellers say 'Don't stop' (2,2)
I believe the answer is:
go on
'sellers say' is the definition.
The definition and answer can be both to do with communicating as well as being verbs in their base form.
Perhaps you can see an association between them that I don't see?
'don't stop' is the wordplay.
I cannot quite see how this works, but
'stop' could be 'go' (going is a kind of stopping) and 'go' is present in the answer.
The remaining letters 'on' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for go on that I've seen before include "Proceed" , "Silly person - bully (US)" , "Harry Secombe, for instance" , "Foolish person - thug (US)" , "Hired thug" .)