Balance sheet
Everything here should be supported by an external source. “External” is not the best term – for example comparing debtors and creditors figures to the aged trial balances is internal to integrated packages – some even compare them for you - you just need to check it. The same applies to stock (inventory).
Bank reconciliations should be a regular part of every business – but one aspect too commonly missed is items entered but never affecting the bank statements. There are a variety of factors here – but these always need to be dealt with ASAP.
I won't go through other options – but every figure should match a figure from elsewhere. This may include figures in other entity's accounts. These might include related companies – but the most common example is a trust. Amounts owing in one should match amounts receivable in another.
There are always exceptions. In this case, the main one is shareholders' current accounts. These can be very busy – although we recommend that you keep private expenses away from the business as much as possible. If you do this, it is relatively straightforward to check the account visually.
Summary
Accounts are your responsibility. So please understand the numbers you see – and if you don't, ask questions until you do.