The only safe "free" Fling trainer is the one hosted on Fling’s official forum thread (usually on the FLiNG Trainers site or a prominent modding community like Wemod or FearLess Cheat Engine ).
In the end, it's up to individual gamers to promote a culture of fair play and sportsmanship, choosing to play games without trainers and respecting the gaming community as a whole. call of duty modern warfare 2 trainer fling free