This can happen for instance when payment is entered in POS and gets recorded in the account History, but before the system has a chance to finish and deduct it from customer’s Balance the computer crashes. In a case like this, the history would show the correct amount with the payment deducted, and the balance would still show the amount before payment.
In a case like this you would select Correct Balance, since the History is correct.
If unsure about what happened, open the Customer’s History, find the point where History shows different than Balance (balance can be seen by going into the Transaction), and see what the situation was to find out if you need to correct the History or Balance. You’ll usually find a transaction or payment with the discrepancy amount so you know where it went off.
For a list of all Account discrepancies open Total Inventory Solutions → Utilities → Check Billing Integrity.