For example, you want to know if your CC has money for your 600$ order.
- You go to a website and choose a random product that costs 600$.
- Procceed to checkout, enter all CC details and a -FAKE- billing.
- Continue and finish the order.
If it will give you a message "Your card has been declined" your card has not enough balance for the order.
If it gives you a message "AVS missmatch" or something familiar, then your card has enough balance.