First conventional sale. Buyer requesting seller credit for closing costs.

[Jorge Leon]

Hi all. My sister is looking to put in an offer on a property in Chicago, first time homebuyer, cosigning with my mother, they have a pre approval letter. I am a new agent and this is my first conventional sale/transaction. Buyer is willing to pay asking price but was wondering if seller could pay for some of the closings costs. What is the norm for buyer to request? The reason I am asking this on BP and not my sponsoring broker is because he is unreachable a few days. I wanted to get a head start. What, if any, is the average credit requested by the buyer? Any guidance would be greatly appreciated.