Most Helpful Guy
You never call a girl a 10, because she will know you are lying. Even if she is a 10 she won't believe it, because every girl thinks she has flaws, even if she doesn't. Some women actually have surgery to get the length of their toes shortened. You can't make that stuff up. With that kind of insecurity calling a girl a 10 is right out.
As far as your friend, even without seeing her I would have given her a 7 or 8 regardless of what she looked like, to try to make you both happy. I mean after all he can't give her a higher score than his own girlfriend, but doesn't want to give her a low score and cause hurt feelings. Like someone said, you really backed him into a corner even if you didn't mean to.