How do you kill the gun store owner?

First go to the stairs by the resturant on the second story when you first come out of the security room. Go halfway up and jump on the blue marquee follow it and you will see a bear a box and orange juice.

Keep following to find an uzi jump down and head toward the store but don't use the uzi. When you get the store you will see a cutscene. Right after jump on top of one of the aisles because he will try to run you over.

When he stops start blasting with the uzi. When you run out of the uzi wait till he stops and jump down to hit him with a sledge hammer or 2 by 4. One or two hits should do.

BE CAREFUL: HE HAS A SHOTGUN

Thats not the right answer if u read the question again it say GUN shop owner ur talkin about the supermarket owner ?

Going after the gun shop owner you have 1 of 2 options Gatling gun or submachine gun are the easiest ways to
Do it

Submachine gun head over to the parking lot grab the red car and head into the maintenance tunnels and when in the tunnels look on your map there should be a rectangular room in the middle head towards that open the black door on the left side the submachine gun waits near the back also if you already havent grabed the maintenance key card it on the opposite side if the room from the submachine gun after that head over to the gun shop and when the battle begins jump out o the gun shop (you may have to deal with zombies out here) and basically shoot the owner from outside the shop

For graving the Gatling gun it just kill the gunner from the convict jeep ignore the others ( dodge around the trees and such the convicts are bad drivers) the make your way to the gun shop just make sure you have at least a hundred rounds of Gatling gun for the boss and do the same thing you would do with the submachine gun