Sometimes the bad guys get the drop on you. Good on the clerk for being prepared and following through with his plan.
The clerk said the robbers put a gun to his head and demanded money, then grabbed a gun he had placed on the counter.
The clerk told police when one of the robbers went to the back of the store, he pulled another gun from his waistband and shot one of the robbers twice. He then shot the second robber as he tried to run away.