OK here are my thoughts on the topic:
Intent is the key word, but only when permitted. If you do something out of the goodness of your heart you will receive good karma, whether is succeeds or fails. On the other hand, if you're doing something because you feel you should, but actually you're meddling in someone else's life, that's bad karma because they didn't ask to be helped. Same as healing someone who doesn't want to be healed.
Karma is 3-fold for a reason. If you kill someone, no matter how hard you work and how good you become through your life you will carry that burden. Some would say "but people change!". My answer is "you should've thought about that before you killed." And linking back to my original point, if you killed accidentally you shouldn't be punished because for all you know it was their time and you were simply the facilitator.
Payment is never on time. I've seen where my good deeds have rewarded me immediately (helping a friend, who succeeded in something she couldn't have before, even with my help). Other times it sort of goes into storage for later. I've had 3 times where my financial situation went south very quickly, and all 3 times money just appeared out of nowhere. I suddenly didn't need to pay a debt or something, and the money it saved me was just enough to get going again.