If you would like to view users who have not yet made a payment or have an outstanding balance, there are a few ways to filter for this, depending on what you want to see.
Head to Users and click the search bar. Click “Payments”. Here you can filter by a few payment related statuses:
You can find all users who need to close their balance, paid something, or have paid nothing (but have a product in their cart).
You can also filter by products, to view all users who have a specific product in their cart, and then add the payment status filter, to view all users with a specific product + needs to close balance / or paid nothing / or paid something.
Additionally, you can always run a Sales report on all or selected products, to view total balances by users. Here is an article on how to do that.