When we do any moral act on the basis of greed, we get merit or sin I am hindu. So 
My  mind  say if you Will help anyone .
 you get rewards for example  job,beautiful wife, health,
Rebirth good place and  rebirth in  healthy human beings.
So I do good act for rewards.

This is also my greed .?
This is sin?
This is good deed?
The Buddha speaks of three sorts of kamma:
Deeds done with the intention to create the experience of pleasure,
deeds done with the intention to create the experience of pain,
and deeds done with the intention to end kamma.

Good deeds, your helpful deeds, are deeds done with the intent to create pleasureable experience. Such deeds will create pleasurable experience.
There is no denying that. Good deeds that produce pleasurable experience tend to result in attachment to the things of this world and the things of this world, being ending things, will result in pain to one who is attached to them. But there is no thing in Buddhism like 'sin'. It is a matter only of personal welfare.

In Buddhism the goal is the ending of kamma, and good deeds are kamma, so the advice for one seeking the goal is not only to eliminate bad deeds, but to eliminate good deeds as well.

Deeds that end kamma are those based on the 8-fold Way. They are intentional deeds of not-doing and letting go. For example, Samma Vaca, High Talk, speaks of training yourself to abstain from saying what is not true. Faced with a desire to get something that is thought to be obtainable only through a lie; one intentionally abstains from that lie. By that abstention from reaction to that desire, that old kamma that resulted in the desire is halted, and that potential stream of kamma that would have resulted from the lie is still-born, dead in its tracks. The whole of the 8-fold Way consists of those places and behaviors and ideas which when followed result in the ending of kamma.