CHICAGO (CBS) — Police on Wednesday were warning the public of a man who has been offering things for purchase in online marketplace, and then robbing prospective buyers at gunpoint, in Woodlawn.

The robberies happened at 6:20 p.m. Friday, Jan. 3, and 9:41 a.m. Monday, Jan. 13, in the 6600 block of South Greenwood Avenue, police said.

In each incident, the victims agreed to buy items through online marketplace applications and came to meet the seller. Upon meeting, the man either implied or took out a handgun and robbed them, police said.

The suspect is described as African-American and between 20 and 30 years old, standing 6 feet 1 to 6 feet 3 inches tall and weighing 140 to 150 pounds, with short black hair and a light brown complexion.

Police advise meeting in a neutral location when purchasing things online.

Anyone with information is asked to contact Area Central detectives at (312) 747-8380.