“Is this understanding correct?” anything more polite than this?

Do we have a more polite way to say “Is this understanding correct?”. I often find it a little tough question to ask to clients.

Anything that sounds more polite and means the same? And also, is the above question grammatically correct?

To confirm whether you have understood the client's issue, the question is fine, if not particularly idiomatic.

So, you have problems A and B, and you need to do C as well. Is this understanding correct?

There's nothing wrong with that. You could alter the question slightly:

Is my understanding correct?
Have I got that right?
Is there anything else?

If you want to find out whether they have understood, you might need to be a little more tangential. For example, don't say this:

That means you will need to do A and B in order that C can be made available. Do you understand?

That may well be considered rude. You'd need to ask about how you have handled the situation.

Have I explained that well enough?
Is there anything else I need to tell you?

I would try "Is my understanding of this correct?". That subtly implies that the possible fault lies with you not them.