Why must auditors put greater emphasis on the completeness assertion when auditing payables? Can this be contrasted with the emphasis in the audit of asset accounts?
Because the likelihood of clients hiding (understating) liabilities is higher than that of understating assets. For assets and revenue, chances are that they will be overstated, so you look out for fake sales towards the year-end.
And what for liabilities ?
For liabilities, you have to perform all those steps to ensure that none are omitted or unrecorded. The emphasis is the opposite of each other, and that governs the audit procedures too.
If they are asking for audited accounts then what they really mean is accounts that have been prepared by a chartered accountant. So find one, pay them to do the work and move on.