Make sure to save your game before attempting this since there’s a lot of factors that can make everything go south really quickly. First, wear your mask and enter the shop. Head straight to the back of the store, ignoring the gunsmith’s warnings and knock on the metal door. The guard behind will tell you that it’s invitation only.
Now, aim your weapon at the gunsmith and press the Up DPAD to force him to open the door. Once he’s walking towards the door and talks to the guard outside, you don’t need to aim with your weapon anymore. This is to lower chance of accidentally firing at him.
While he’s talking to the guard, approach him to whack him unconscious then aim your weapon at the startled guard. Keep interrogating him until he tells you to check the room in the third floor. You can leave him without any issues.
Proceed to the third floor. There’s an armed guard inside so you’ll need to rush towards him with your weapon drawn (NOT AIMED) then press Circle to melee/whack the guard down. The players will be surprised, with one of them attempting to cover the safe.
Get the money on the table then you can threaten the two guests on the floor. When done correctly, they may even ask the player by the safe to open it for their safety. If the players escape, don’t bother blowing up the safe with a dynamite since the noise will alert everyone outside and the contents are not worth the risk of raising your bounty. You can also loot the other items inside the room, including a pack of premium cigarettes. You also need to do this quickly since lawmen will arrive shortly after.
Unlike other stores where you can only leave through the front door, you can jump to the back alley from the third floor veranda. You’ll suffer damage but it won’t be fatal. Remove your mask and leave the search area to safety. If done correctly, you’ll get away scot-free without any bounty.