...to prevent robbery, how can you purchase weapons and how does the Vendortron restock?

I would imagine there some kind of chute to place weapons in and out. This been brought up before but I can't remember what people said. There may even be a comment about it in game.

I believe there is supposed to be a tunnel from the workshop to the kiosk. As for the weapons, they could be delivered through a slot much like banks have, or they could be brought out for you by the workers. I don't remember what the consensus was for the purchase delivery.

The tunnel could be sussed out by making a hard save point, then going in and raiding the gun runners workshop and seeing what is there.

Aye, they certainly do protect their stuff well. Thanks for the answers.

I don't remember it being brought up in game, but I've never infiltrated the building so yeah.