This is the most important question. The general rule is: Legitimate, commercial services like PLITCH offer vetted trainers with a subscription model, ensuring a completely safe, ad-free experience. For free options, the onus is on you to vet the source. A file from a forum post with zero comments is exponentially more dangerous than a well-known creator's release on a major site.
Most trainers utilize a numeric keypad system (Numpad 1–9). When you press a hotkey in-game, you should hear an audio chime confirming that the memory hack was successfully applied. Crucial Safety Notice: Single-Player vs. Multiplayer sniper elite 3 trainer all version full
Locks your bullet count. You will never run out of rifle, pistol, or submachine gun ammunition. This is the most important question