Safety experts warn about the potential dangers of buying and selling through apps

— -- The rise in popularity of apps that you can use to buy and sell things online is causing safety concerns from experts and local police departments across the country.

"Anytime you're dealing with strangers your risk level of something bad happening goes up," Steve Kardin, a former police detective, told ABC News.

"This really is the new marketplace," Kardin said of doing business through apps, which many see as an easy and fast way to make cash by posting an item you want to sell and then waiting for the highest offer.

Kardin said the safety concerns arise next, when, "you agree to meet at a specific location."

Pooja St. Amand, of Middletown, Connecticut, told ABC News that she was robbed after meeting up with a stranger when she was selling an iPad through the app OfferUp. St. Amand said she took what she thought were all the right safety precautions and she agreed to meet the potential buyer in a populated community center parking lot.

"My whole body went numb, I was scared," St. Amand said of the incident. "The only thing that they didn't take was my personal cell phone and the iPad that we were selling."

The threat of crimes related to these meetings have sparked police departments across the country to set up designated safe meet-up spots for doing business through apps, many of them located in the parking lots of local police stations.

"Criminals do not want to commit crimes at the police department," Frank Sabol, a Port St. Lucie Police Department sergeant from Florida, told ABC News. "They know that their likelihood of being arrested or getting caught greatly increases."

The Rocky River Police Department of Ohio announced their new meet-up spot outside their police office on their Facebook page, saying in a post that not only will the new location reduce the risk of fraudulent transactions, it will also "let buyers and sellers avoid giving personal information, such as home or work addresses, to complete a transaction."

The Fanwood Police Department of Fanwood, New Jersey, which also has a meet-up spot right outside of their police headquarters, noted in a statement announcing the location that it would be monitored 24 hours a day with surveillance cameras.

OfferUp told ABC News in a statement that they have provided close to 5,000 signs to police departments across the country, and "are committed to providing local buyers and sellers with the best experience possible and safety is a big part of that."

They also released a series of safety tips which includes reviewing buyer and seller profiles before making a transaction, communicating with strangers only through the app, putting extra care into where you choose to meet up and bringing a friend or family member if you have to do a transaction at a private residence.

A spokesperson for another popular app for buying and selling, letgo, told ABC News that "Tens of millions of people securely buy and sell billions of dollars in secondhand items on letgo every month," and they "constantly test new ways to ensure our app remains a safe place for local buyers and sellers to connect."

"We use human and artificial intelligence to moderate our marketplace and we ask our user community to flag anything or anyone that raises concerns in extremely rare cases where that's necessary," the spokesperson for letgo added.

Kardin advised that if you choose to meet somewhere other than a local police department parking lot, there are three key things you should ensure before meeting up with strangers, including that the location is a public place, has a lot of people around, and has surveillance cameras.