Flattery seldom works with discerning people. It is shallow, selfish and insincere. It ought to fail and it usually does. True, some people are so hungry, so thirsty, for appreciation that they will swallow anything, just as a starving man will eat grass and fishworms.
The difference between appreciation and flattery? That is simple. One is sincere and the other insincere. One comes from the heart out; the other from the teeth out. One is unselfish; the other selfish. One is universally admired; the other universally condemned.