The seller met two people at his home about 8 p.m. in the 33000 block of 22nd Place South.
Instead of purchasing the phone, the people tried to steal it and fled on foot, police spokeswoman Cathy Schrock said, based on preliminary reports.
The seller chased them, struggled with one person, and then one of the people shot him, Schrock said.
The man shot is talking to police, and his injuries are not life-threatening.
Further details were not immediately available.