How to get better at scoping?

Hey, was just wondering if anyone had some good resources/books on how to get better at scoping with clients.

Not over hours yet, however just had a client request two changes that will cause a lot of rework. This was after they finally brought in the person that will be using the product. I know stuff like that is just out of our control… but I dunno. Guess I'm just looking for tips on how maybe one could suggest or nudge the client towards the right way at the start lol.

Thanks for any help!