When a buyer asks for seller to pay closing costs...

[Carlos Rodrigues]

When a buyer asks to pay for all closing costs, exactly what would the seller be paying for? And how and why would a seller even agree to such thing? On a duplex of  approximately $350,000 in NJ how much would the seller be paying for at closing having this requirement? What about the buyer?

Thank you in advance and I'm sorry for such a lame question. I'm new to real estate and gaining knowledge is my ambition. Thank you for understanding and guiding me in advance!!