Here is a scenario which has not happened to me (yet!) but I have been thinking about recently.
Very profitable Business incorporates.
Accountant assists client with goodwill valuation, and a substantial directors loan account is created. The valuation utilises a multiple of owners benefit of 2-3 times.
Amortisation is claimed as a deduction in the company P&L.
Some years later the company successfully disposes of the business to a third party for eight times profits. A substantial corporation tax bill results.
The director is unhappy as he has sold the business to the company too cheaply. Overall the company and director have paid more tax than the optimum amount.
Director sues the accountant.