1. The Internal Revnue Service writes letters and notices to you before they reach out to you by phone. So if someone calls and tells you that they are from the Internal Revnue Service and you have no contact then it is unlikely that they are from the Internal Revnue Service.
2. The scamers have been asking for money in a short time span. They often ask for the money in just a few hours.
3. The Internal Revnue Service has options to repaying back taxes and there are repayment plans or it could found to be non collectable.
4. The Agents for the Internal Revnue Service will meet with you during normal business hours. The scamers are contacting people at night and weekend.
5. The numbers to the Agents for the Internal Revnue Service are printed on their cards and they meet with you. If the Agents can't meet with you then they will likely leave a card with your office or even on your door. They don't just start collecting without many notices.