If a non-believer says Salaam, he gets good deed for this?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Allaah, the Exalted, set a condition for the acceptance and reward of deeds, and that is faith, Allaah Says (which means): {And nothing prevents their contributions from being accepted from them except that they disbelieved in Allaah and in His Messenger and that they come not to prayer except while they are lazy and that they do not spend except while they are unwilling.}[Quran 9:54]. Moreover, the Prophet set a condition of being a Muslim in order to enter Paradise, as he said: "No one will enter Paradise except a Muslim person." [Al-Bukhari and Muslim] Therefore, it becomes evident that a non-Muslim will not be rewarded on the Day of Judgement for the good that he does in this world. However, as Allaah is Most Just and Most Merciful, he recompenses him for his deeds in this world. It is confirmed that the Prophet said: "When a non-Muslim performs any good deed, he is rewarded for it in this world; and in the case of a Muslim, Allaah stores up his good acts for him in the Hereafter and provides him with subsistence in this life due to his acts of obedience." [Muslim]

Therefore, if a non-Muslim greets a Muslim by saying 'Salaam' he will not be rewarded in the Hereafter for this act. If a disbeliever greets you with Salaam, then you should limit your reply to saying: "Wa 'Alaykum" and not the full response of Salaam.

Allaah Knows best.