A totem pole of experience, knowledge, and authority exists in dealing with different Divisions of the IRS. Automated notices are usually the first thing a delinquent taxpayer will receive. This comes from the Automated Collection Division of the IRS. These usually take the form of notices reminding a taxpayer to file unfiled tax returns, and progressively get nastier unless some type of response is made by the taxpayer to get their situation handled.
After that the Collection Division will kick into gear. These notices state specific things will happen, unless some response is made from the taxpayer. If the taxpayer has not filed, and continues to not file after being told to, the IRS will file a SFR, or Substitute for Return for you. Once the assessment of tax is made, the Collection Division can go after your paycheck or bank account.
In situations where no response is made by the taxpayer, Revenue Agents may step in. This is usually a very serious matter, and a taxpayer should always seek Professional help when this happens. The ante has been increased, as an IRS Revenue Agent may send you a summons, put a lien on your Social Security number, which attaches to all property you own, issue a Bank Levy, or Wage Garnishment. If you are self employed, they may force you to disclose who you are receiving payments from, so they can force them into paying the IRS.
Even though it seems all is lost once a Revenue Agent enters the picture, the opposite is often the case. IRS Revenue Agents also have the most knowledge of the employees at the IRS. This can be used to the advantage of the taxpayer, utilizing the experience, knowledge, and understanding of IRS Precedent, with a Tax Professional who is adept at solving these types of problems.