A warning Facebook users need to know: thieves are using popular online yard sales to make a quick buck on stolen items.

Police said the crooks pose as interested buyers, but when they meet up, they take off without paying.

For some, it's a matter of convenience, posting and selling almost immediately.

"eBay, you know, you can start a bid, and it takes a week, or you can put it on Facebook or Poshmark and it be sold in an hour," Christian Allee said.

Instead of laying items on your lawn, you post them online. Buyers scroll through and meet you for the sale. Allee knows them well. He uses these sites to buy broken phones.

"Anywhere from fixing the screens, to home buttons, to volume buttons, power buttons," he said.

However, not everyone shopping has good intentions.

"People are meeting up with strangers online, and they're trying to attempt to make a transaction and end up getting robbed," Detective Terry Barnes, Chattanooga Police Department explained.

CPD is seeing more of these crimes and provided us with some of the locations where the transaction did not go as planned.

We went to six different locations where an online exchange turned into a robbery. Most were in public locations, but all of them had little or no surveillance video, leaving sellers out of luck.

"They're using their home turf to decide where these transactions take place, and they already have some sort of layout of the land and know where they're going to run to after they commit these crimes," Barnes explained.

If you sell online, Barnes said you should go to a well-lit public place. One option is the department's "Safe Exchange Zone," which is in front of their building on Amnicola Highway and is watched around the clock.

Barnes said if your buyer doesn't want to meet there, then it's probably a red flag for you not to do business with them.

This year, there have been 86 robberies from persons, some were from online exchanges. Barnes says electronics and cell phones are the number one stolen item because of the resale value.

If you sell online, use caution and go to a safe location.

"Meeting someone online is always going to be an unknown; there's always going to be some unknown factor there," he said.

The area is available for use 24 hours a day and can also be used as a safe and neutral site for child custody exchanges.

Experts say if you're buying a phone online, you can check to see if it's stolen by checking the IMEI number online. If the number was reported stolen, the phone will not work.