Gta 4 why does the ammo guy is shooting at you?

Answer 1

As long as Niko behaves himself in the ammo stores, just goes in, buys his weapons and leaves peacefully, he will have no problems with the store owner. But, if Niko starts waving a weapon around, aiming at the guy or start shooting, then the store owner will usually start firing, often joined by some of his friends, who will come and back him up.