When a lawyer or accountant discovers that a client has made an error (e.g., treated certain sales as tax exempt when they are actually taxable), they may recommend that the client make a voluntary disclosure. Assuming that the disclosure meets the administrative criteria of the tax authority as being voluntary (which is an entirely other problem), the hard part is "getting to 'Yes' with the auditor".
The voluntary disclosure must be complete and accurate. The auditor operates under the mantra "accept, but verify". If the person making the disclosure leaves out important information that they do not want the auditor to know, they may be fooling themselves and not the auditor. The auditor may discover those secrets during a desk audit or an on-site audit. The factual circumstances may not make sense to the auditor if part of the story is missing and the auditor will dig further. Do not assume that the auditor will accept the cheque on behalf of the government and not have a single follow-up question. That never happens.
When a business makes a voluntary disclosure, they often do so to avoid paying the penalty that is charged when an auditor finds the mistake. In return for not charging the penalty, the government wants a complete and accurate disclosure of the relevant facts in order to be in a position to determine that the business is coming in to full compliance. Essentially, in a voluntary disclosure, you do the work for the auditor and the auditor quickly reviews the work (and in the case of correct disclosures, simply agrees with your worksheets).
Voluntary disclosures can be problematic when this simple review stage cannot take place because the information is not provided. In many cases of voluntary disclosures by inexperienced persons, there is no intentional wrongdoing, but the disclosure is not complete because of the inexperience. The auditor wants certain information and if the person making the disclosure does not understand the task at hand, or the sales tax regime, or the facts that are relevant or the documentation that will be relevant, etc., the good intentions of the voluntary disclosure can turn into a big and costly mess.
It is kind of like that home renovation project that started with a beautiful photo in a magazine and when you did it yourself to save money, it ended really badly and was much more expensive. Or, you hired a cheap contractor who did not have experience renovating bathrooms, but took on the project, and ran into problem after problem after the demolition phase. Part way through the project, you could not turn back and go back to the status quo.
Consider sales tax specialists as a "Mike Holmes" of voluntary disclosures. Professionals who have done this before plan ahead. They use their knowledge to investigate the potential issues BEFORE moving forward with the project. They develop a plan that is tried and true. They help you be reasonable in your expectations. They work with you so that the results are successful and within the planned budget.
Many sales tax lawyers who have helped many clients make voluntary disclosures have precedents that they use to prepare the voluntary disclosure. They know the statutory provisions, the case law, and the tax advisory opinions that apply. Sales tax lawyers are able to help you gather the facts and communicate the facts correctly. They can anticipate the follow-up questions and include the answers in the disclosure. They can help you organize the applicable documents and the documents that the auditor likes to review in the normal course.
Getting to "yes" in a voluntary disclosure means meeting the auditor's expectations and needs. The auditor must put together a report for a supervisor. You must give the auditor what he/she needs to get that approval.