Getting a call from the IRS can be pretty uncomfortable, especially if the caller starts demanding money on the spot. Legitimate IRS representatives won't do that, but the criminals impersonating them do. Scammers pretending to be IRS agents steal money and personal information from their victims. Luckily, it's pretty easy to tell impersonators apart from real IRS agents, as long as you know what signs to look for.
For instance, if someone calls you out of the blue and threatens to arrest you unless you pay your taxes, it is not the IRS. The IRS will only send you notices by mail. Recently, scammers have sent emails that link to a fake IRS website, but remember, the IRS does not initiate contact via email.
The IRS rarely makes house visits, but if you do receive an unexpected visit, make sure to request credentials. IRS agents will always have 2 official credentials - a pocket commission and an HSPD-12 card. They should also be able to provide you with a phone number to verify their identity.
Lastly, the IRS will only accept payments made to the U.S. Treasury. If someone asks you for payment in pre-paid debit cards or gift cards, it is a scam. You can report incidents like this to the FTC. For more information on verified payment methods, visit the IRS website.