Says it’s bad but cooks it (6)
I believe the answer is:
roasts
'says' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how they can define each other.
'it's bad but cooks it' is the wordplay.
I cannot really see how this works, but
'it's' could be 'ts' (abbreviation. e.g. in 'tis) and 'ts' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for roasts that I've seen before include "gets very hot" , "traditional Sunday food" , "Cooks meat in oven" , "Has a go at" , "Cooks in dry heat" .)