The shoe salesmen made a couple of basic mistakes. For a deal like that you meet outside the police station or in the foyer of City Hall or some such. Outside an abandoned house? Not the best place.
They should have considered the numerous violent robberies and murders that have occurred for trendy shoes.
They knew they were dealing with teens when they talked to them on the phone.
Second degree? They brought a gun to a simple shoe deal. Why did they bring the gun? Teens will kill you for your shoes.