There are hundreds of millions of transactions that happen safely on Craigslist, but like some many other sites, there are those who want to use the site to commit crime.
Philadelphia Police have identified one of the criminals and are working to identify two others.
Philadelphia Police are looking for a man connected to a rash of robberies hatched on the highly popular online classified ad site, Craigslist.
He is identified as Aleem Reed, and he is still at large.
Last week police say he asked a man who was selling an expensive Rolex watch to meet him in the 1400 block of Jefferson Street in North Philadelphia to make the transaction.
"During the course of showing the watch, a second male or the male that was buying the watch, produced a handgun and announced a robbery, and took the watch," explained Lt. Ray Evers.
A few days later in the 1900 block of Gratz, a man who identified himself as a Temple student, asked a guy trying to sell a $7,200 Rolex to meet him there to make the transaction.
But Police say while the buyer was looking at the watch, a second man identified as Aleem Reed approached, pulled a gun and announced a robbery, took the watch and fled.
Police say another incident happened at the same location.
"Basically, the same M.O. happened every time, they would contact someone on Craigslist in reference to purchasing a high end piece of jewelry or a watch," said Lt. Evers.
In the most recent incident, the suspect attempted to buy a Movado watch from a seller who refused to hand over the watch when the second man threatened him with a gun.
Police say the thieves shot the man in the leg and took the watch.
"The buyers and sellers have to beware," said Lt. Evers. "The meeting place is very important."
Craigslist says it had over 573 million postings on its North American website last year, so the odds are miniscule that some are going to be associated with crimes.
And while it may be a wonderful, useful tool for buying or sell stuff on the internet, police are issuing warnings to internet users.
"Be very, very mindful of your surroundings. Do as much homework as you can on that potential buyer or seller," Lt. Evers said. "I mean, make sure you go to a place that you feel safe and bring someone with you. Make sure someone knows where you are, and go to a very, very public place to make that transaction."
Officials suggest some place like 30th Street Station in Philadelphia, or a police district, but never in some isolated street or location you are not familiar with.
Police are also looking for help locating Aleem Reed, and are asking anyone with information to contact police or call 911.