I tried wasting my ammo and could buy AK/VSP and all stuff with CH trainer aswell... There's no need for a savegame . Just waste your ammo, it will take some time... and then you will be able to buy anything.
another bug i ran into, which my brother also ran into on his xbox version that he didn't cheat on, was that i could not pick up any gas mask filters. i could buy them and i could receive them from NPCs, but i could not pick up the ones i found in the environment. making the last portion of the game from the library on, very difficult.