Lucky Charm (up to 6) will give you an increased chance of lucky finds. This will give you a chance to find top-quality items in any random container (chests, barrels, baskets, skeletons, etc.) It should have no effect on vendors or loot drops from monster kills. If you get a lucky find then the animation should always appear. However, as Furin noted in another discussion, Lucky Charm does seem to have an odd way of making people luckier... Gambler's Fallacy?