wouldn't you say

butter wouldn't melt in someone's mouth

The identified person appears to be benign, mild-mannered, or calm (but with an integral suggestion that, to the contrary, they really are untrustworthy, disagreeable, or mean-spirited).

final say

The right to make a final decision.

have a say

To (receive the opportunity to) voice one's opinion.

I'd say

It is my estimate or opinion.

I'll say

Used to indicate emphatic agreement

let's not and say we did

Indicates that the speaker does not agree with a proposed action, and does not wish to participate.

needless to say

Clearly, obviously.

say again

"What did you say?" or "Repeat what you have said." A polite formula used when one has not heard or understood what has been said.