Some VAT mistakes invite attention faster than others, and most are avoidable. The first is a return that does not agree with bank deposits, because turnover should reconcile broadly with the money hitting the account. The second is claiming input credit on invoices that the supplier has not reported, a mismatch the department detects instantly and investigates. Third is the habit of under-declaring cash sales while treating every expense as VAT-paid, a pattern that produces suspiciously thin margins. Fourth are returns filed late repeatedly, because even when the arithmetic is right, serial lateness marks a file as worth visiting. Fifth is changing classifications, treating taxable goods as exempt whenever a discount is useful. Sixth and seventh are the bookkeeping failures: no proper invoices retained and no register linking each claim to source documents. None of these are fatal if corrected early, and the response to an audit letter is not panic but preparation. Assembling the purchase register, bank statements and supply records in one file lets a business answer the points raised within the time limit and avoid the compounding that follows silence.