If you work at a store and some customers come in trying to put thousands of dollars on prepaid debit cards, you’d probably get the sense that something is amiss. The question is: Do you do anything about it or just help them put the money on the card and hope they aren’t being scammed?

The well-trained scam antenna of an employee at a Safeway in Rockville, MD, went up when she recently spotted a couple of shoppers trying to get $4,000 worth of prepaid debit cards.

When she asked them about why they were putting so much money on the cards, the customers said they’d been contacted by IRS agents who claimed they had to pay thousands of dollars right away in order to stop an IRS investigation.

“I said, ‘Don’t buy it, it’s a scam,’” the Safeway cashier tells WJLA-TV [via Credit.com]. “They had a whole wad of money like you wouldn’t believe. And they said, ‘Thank you, thank you, thank you.’”

Unfortunately for the couple, they had already been scammed out of $3,000 by the bogus IRS agents, meaning somewhere there’s a cashier who didn’t notice the obvious red flags that a scam was in progress.

More and more retail employees are being trained to identify the telltale signs of these tricks, which often require victims to pay in either wire transfers or prepaid cards.

If the IRS believes you owe it money, you will get a bill in the mail. The agency will not call you and tell you that you need to pay ASAP and that the only way you can do so is with a reloadable debit card, nor will they ask you for credit or debit card information over the phone. The IRS will also not threaten to have you arrested for lack of payment.

If you get one of these calls, hang up. If you aren’t sure it’s a scam because you do actually owe taxes, call the IRS at 1-800 829-1040.

If you know you don’t owe taxes, report the incident to the Treasury Inspector General for Tax Administration (TIGTA) at 1-800 366-4484 or at www.tigta.gov.

Regardless of whether you owe or not, you should file a scam complaint with the Federal Trade Commission via the online FTC Complaint Assistant.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.