A perfectly balanced trial balance, with no suspense account, does not mean that your accounts are 100% accurate. There may well be errors within the accounts. A trial balance that is balanced only proves that the total of the debits matches the total of the credits. Any error which has an equal and opposite debit and credit will not cause the trial balance to become imbalanced. Therefore the error will not be highlighted by the trial balance.
In the exam you will be told what the error was, but you need to decide if you need a suspense account. You will also need to be able to remove the suspense account, if there is one, and correct the original entry.
These skills are needed at all levels of accountancy, and come up in all levels of the AAT qualification. Students do find these types of questions difficult as all errors are different; you will need to think on your feet. The key to these type of questions is to think “what went wrong” and “what should have happened”. Then the difference between them is the journal you need to enter. It helps to draw up T accounts on paper and lay out what was originally entered.
View the online lecture where we look at the different types of error that do not require a suspense account.
We also have a corresponding blog on errors which do require a suspense account here.