Doing Favors (〜てあげる・てくれる・てもらう)

These two sentences describe the exact same event from opposite sides, exactly like plain あげる and もらう did with objects. てあげる puts the giver of the favor as the subject; てもらう puts the receiver as the subject, with に marking whoever did the actual favor.

てくれる always centers the speaker, or someone close to the speaker, as the one benefiting, which is why 予約してくれました naturally implies “for me” even without saying so directly. Compare 予約してあげました, which would instead describe the speaker doing a favor for someone else.

Careful with あげる toward someone above you socially, saying してあげました can sound like you’re bragging about the favor. くれる and もらう carry no such risk, which is why they’re used more freely across all levels of politeness.