Baldwin Park police had received a tip about a Craigslist advertisement of N95 respirator masks for sale.

The listed price for a single box of 20 masks, which are currently in short supply in hospitals across the nation during the new coronavirus pandemic: $300.

Detectives wearing plain clothes and posing as buyers contacted the man behind the post and met with him on Tuesday morning at a shopping center parking lot in West Covina, police said. As a part of the ruse, the detectives exchanged the cash for the box. Then they immediately arrested the man on suspicion of price gouging during a state of emergency.

Investigators also seized a stockpile of 420 additional N95 masks from the suspect, who police identified as Johnwill Baldonado, 30, of Covina.

District attorneys throughout Southern California have been warning residents about price-gouging schemes that exploit the public health crisis, saying they are ready to prosecute people who resell essential items, such as certain equipment, food, fuel, or shelter at a rate 10% more than its typical market price.

With masks, particularly N95 respirators, in short supply, the protective gear has become a potential cash cow for would-be price gougers, and a source of concern from healthcare workers who have felt the shortage most acutely.

Last week, the Centers for Disease Control and Prevention recommended that people should wear face coverings when in public to help prevent the spread of the coronavirus. But federal officials stressed that surgical masks and N95 respirators should be left for those on the front lines of fighting the spread of the infection.

Some healthcare workers in Southern California have said they fear for their safety while caring for patients infected with COVID-19, voicing concerns toward inadequate supply of proper protective gear, such as N95 masks, inside hospitals and clinics.

The federal government on Monday struck a deal with manufacturer 3M to produce 166.5 million masks over the next three months to help support healthcare workers in the U.S.

Such shortages have also prompted online retail giant Amazon to ban the sale of N95 masks, noting to customers that the items are being prioritized for hospitals and government organizations.

Amazon has long been cracking down on users who attempt to price gouge.

A search for “N95 masks” on Google’s shopping hub yields zero results. The site shows a “COVID-19 alert”: “Product availability may be limited, and we’ve removed results with excessive price increases.”

The hundreds of the coveted masks seized Tuesday from the Covina man are currently sitting inside the evidence room of the Baldwin Park police station with the decision of their fate to come on a later date, said Baldwin Park police Lt. Chris Hofford.

Hofford said that to release the masks, police would need a court order. He said the masks may be put to use among its own officers, who are required by department brass to wear N95 masks when on patrol, or could be donated to hospitals.

“We definitely want them to be put to use given the current pandemic,” Hofford said.

The suspect, Baldonado was booked at the police station on suspicion of the price-gouging violation, a misdemeanor, and was released from custody with a citation and order to appear in court, Hofford said.