Is there an idiom or saying for someone asking the same question many times in hopes of a more favourable answer?

What is the idiom or phrase to describe someone fishing around by asking the same question to different people until they get the answer they want? Like when someone asks a sales person if there are any specials or discount, and the answer is no. So they go ask someone else the same question hoping that if they ask enough eventually someone will tell them what the wanted to hear first time.

Similar to the phrase “asking the same question won’t get you a different answer”. It’s usually used to describe kids asking the same question hoping that someone will say yes. Almost like not wanting to accept reality, and trying to convince yourself you can when you know you can’t, but ask anyway because eventually someone will give you the answer you want, even though it won’t change the outcome.

So say a child does not want to drink water, but they have heard plenty doctor’s and teachers and parents say that you HAVE to drink water else you’ll die. They already know that’s true but don’t want to accept it. So they get clever and ask around, constructing the question in such a way that eventually someone will give them the answer they want to her. So instead of asking if they can drink juice instead of water and not die (because they know the answer will be no) they ask “Mom, instead of drinking 6 cups of water a day, can I drink 18 cups of juice a day instead?” implying that the fluid content in 18 cups of juice will be equal to the fluid content your body requires from the 6 cups of water everyone says you need.

I hope my question makes sense?