To flatter is to give too much praise, to compliment unduly. By its very nature it is insincere, not an expression of honest opinion. If, however, we imitate a person – that is, do as he does – we are paying them a sincere compliment.
‘My neighbour on the left thinks I made a magnificent job of returning our front lawn; he can’t speak too highly of it.’
‘What about the chap on the other side? Is he full of praise too?’
‘No; but as soon as he saw how mine turned out, he began to return his own.’
‘They say that imitation is the sincerest form of flattery!’