The signs of Mr Elton's poor character is not that obvious, what annoys me is that Emma fails to notice any sign that Elton was courting her and not Harriet.

John Knightley said in chap 13 --
"I never in my life saw a man more intent on being agreeable than Mr. Elton. It is downright labour to him where ladies are concerned. With men he can be rational and unaffected, but when he has ladies to please every feature works."

"Mr. Elton's manners are not perfect," replied Emma; "but where there is a wish to please, one ought to overlook, and one does overlook a great deal. Where a man does his best with only moderate powers, he will have the advantage over negligent superiority. There is such perfect good temper and good will in Mr. Elton as one cannot but value."

"Yes," said Mr. John Knightley presently, with some slyness, "he seems to have a great deal of good-will towards you."

"Me!" she replied with a smile of astonishment, "are you imagining me to be Mr. Elton's object?"

"Such an imagination has crossed me, I own, Emma; and if it never occurred to you before, you may as well take it into consideration now."