ok, n00b...
feedback = iGiver (left after a transaction with invites, bonuses or seedboxes)
rep = green bars under your progress bar (given by clicking the "sheriff's star" on the left bottom corner of each post)
rep and feedback are totally different things.
you can give multiple iGivers for the same person, just not for the same invite. no matter how many invites or stuff you give to the same user, your Feedback Score will only increase just once. the rest of the feedbacks are "archived". to make it blatantly clear, Feedback Score number shows the number of different guys you have dealt with.
also, you can't give rep for the same post more than once. if you really-really liked someones post and think he deserves more, then you better gain some rep yourself

. the more rep you have, the more you can give.