Howard County police are warning about how and where residents decide to complete an online transaction in person.County police said what started as online sales have turned into one armed robbery and one carjacking. In both cases, suspects have yet to be caught and the stolen goods have yet to be found.Police said a man arrived around 10 a.m. Sunday in the 6000 block of Majors Lane in front of an elementary school in Columbia to buy a phone he found online. Instead, the purported seller pulled out a gun and stole the man's cash."When you're involved in an online sale, it's very important to very cautious," Howard County police spokeswoman Sherry Llewellyn said.Police said the robbery happened less than a day after a carjacking in the 9100 block of Baltimore National Pike in Ellicott City."When the victim arranged a test drive, the suspect got in behind the wheel, and after the test drive, took off in the car on her own," Llewellyn said.The Howard County Police Department has set up safe transaction zones at several of its stations. There are two designated parking spots right up front, and the police station lobby is offered as a third location."If someone is involved in an online sale with you and they are not willing to come to a police station to make the transaction in person, that should be a red flag that it's probably not a safe idea to engage with this person," Llewellyn said.If a crime does occur in a safe zone, the exterior of the facilities are monitored by video 24 hours a day, seven days a week.