[GTJ]

Middle school is around where natives learn the higher respectful forms, I believe. My girlfriend gave me one of her 中学生 level books and that's all it was. So if you wanna go the native route, that's probably where you'll start.

Companies do their on training to "fix" everybody's keigo, because a huge percent of Japanese youth have it all wrong anyway.

I used Genki to study keigo. It's hard no matter where you look, but I like the way Genki lays things out.

I also thing it's pretty tough to get feedback because a lot of the time it's a very subjective thing; even though there are set rules for how to form a keigo sentence, like I said, even the Japanese have a hard time with it, so you'll probably get mixed comments from native speakers.

Good luck (to your friend)!