Useful expressions

STOP saying "WHAT?": Advanced English Lesson (Vanessa)

Ways to say "What?" - Be Polite in American English (Rachel)

What? What did you say? May sound rude.

The better are:

Excuse me?
Pardon?
I beg your pardon? (Old style, but still in use, be careful with intonation)

Sorry, what'd you say? (= What did you say) (you weren't completely paying attention)
Sorry, can you say that again? (there is a lot of noise and you can't hear...)
One more time? = Can you say that one more time?

I am sorry?
I didn't understand. Could you repeat that?

Sorry, I didn't catch that.
Sorry, I didn't catch that. Is it possible to repeat that last point?
Sorry, I didn't quite catch that.
Sorry, can you repeat that please?