This mission is as hard as it is to pronounce the name. At first, rush out to the front with the manager and take out the goons. After you've killed the last one, follow the manager around to the side and rush up on the terrace taking out the first car as you go. Once up there, take out the cars and the vans they turn up. Blind rage is a good at this point.
Once a message flashes up "Regroup inside", get inside and make sure you're first going down the stairs, as sometimes there will be a couple of guys at the bottom who will make short work of the manager. Once inside, all you have to do is fend off the attacks from the three entrances. Pay close attention to the radar and watch out for the manager.
The most effective way is if you have a rocket launcher. Simply shoot at the vehicles and make sure there's no more left, even if the manager goes inside. Once there are no more vehicles, use your machine gun to take out the remaining enemies outside until the manager is safe.
For the Wii version, use to quickly turn around and shoot the guys behind while you're inside. The only warning is to not use rage at this moment because you might hit the manager by accident and have to start all over again.
You can now buy the store for $2,000,000. If you have Montana Holding it will cost you $1,800,000.