you can say that again

come again

A polite formula used when one has not heard or understood what has been said, or to indicate surprise.

do exactly what it says on the tin

To do what is described or what one would expect, with no further explanation needed.

easier said than done

Easy to propose, but difficult to accomplish.

final say

The right to make a final decision.

have a say

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

here we go again

An expression of frustration upon seeing or hearing something bad repeated.

I see, said the blind man

Expressing confusion.

I'd say

It is my estimate or opinion.