I think everyone responds to GENUINE acts of kindness.
Genuine kindness is doing something for the sole benefit of someone else.
But usually to a girl, BEING KIND = WANTING THEM.
Girls, and hot ones especially, are used to guys doing nice things for them. Most guys simply want to get in the girl's panties.
Therefore, girls will always suspect an ulterior motive to any kind act from a guy towards them.
The hotter the girl, the less receptive she'll be, coz she used to guys hitting on her ALL THE TIME.