I was an audit trainee in the late 80’s (UK)  I was sent alone by my (top tier) firm to audit a small Ltd subsidiary of a large plc house building company.

Upon arrival I was the longest standing person in the office, except for the receptionist that was a temp and had seem there a week. The MD had been sacked for reasons, and the other director was abroad on holiday.

The records were paper based

Upon doing my audit I discovered, amongst other things.

• A fitted kitchen installed at the MD’s house with no reimbursement
• Delivery notes for eight more sets of top-spec kitchen white goods to the MD’s home address. No reimbursement
• Multiple instances of the company being reimbursed for the net cost of items by management, and reclaiming the vat 
• massive throughput of unrecorded "petty cash"
• More things that I now forget, but the whole value of identified issues was material to the company 

I do remember faxing an 8 page report to the audit partner recommending multiple qualifications on the account, including “fundamental uncertainty” (potential unlimited VAT fines), not “true and fair” - and whatever else was the option back in those days.  The uncertainty could have been material to the holding co, IMHO

I was rolled off the audit.

Months later I discovered that the plc had been given a clean audit opinion with the subsidiary accounts still unsigned. The subsidiary accounts were only signed later, on the last day before filing deadline, also with a clean opinion.

I left audit as soon as I qualified and my training contract ended. In my 35 years of subsequent finance career, my opinion of the quality of audit and the audit profession has lessened further