N2
確かに
たしかに
Surely, Certainly
確かに彼はイケメンですが、マナーが悪いです。
He is certainly handsome, but he has bad manners.
Explanation
「確かに」 has 2 uses
1Certainly
Confirms that something is true: 「確かに荷物を受け取りました」 (I did receive the package).
確かに彼は信頼できます。
He certainly is reliable.
確かにさっきのは言い過ぎだった。ごめん。
What I said earlier was certainly out of line. I'm sorry.
2True, but…
Grants a point first, then 「が」「けれども」「しかし」 brings in your own view: 「確かに高いが、性能はいい」 (it's expensive, sure, but it performs well).
確かに彼はイケメンですが、マナーが悪いです。
He is certainly handsome, but he has bad manners.
確かにこの店は安いが、サービスはよくない。
This shop is cheap, I'll give it that, but the service is poor.
Mixed up with
「確かに」: certainly, no doubt.
「確か」 (without 「に」): a guess from memory, 'if I remember right': 「彼は確か来週帰国するはずだ」 (I think he returns home next week).
The two differ in meaning; do not mix them up.