Innocent error: agent's failure
Taxpayers cannot wash their hands of responsibility for the correctness of the account by saying that errors, omissions or understatements of value are due to poor work by an agent.
You should ask what personal checks they carried out before signing the account. If the taxpayer signed the account without even reading it through that could in itself amount to negligence. We also expect a taxpayer to check that the agent made full and appropriate enquiries of third parties where necessary and has taken into account all information given to them before the account is delivered.
You should point out to taxpayers that that they signed the account and made a statutory declaration that it is correct and complete and even if someone else has completed theform they remain responsible for its accuracy.