OK...each state is different but the first thing you need to do is read your real estate sales contract BEFORE you sign it and until you understand it don't sign it!
Now to closing costs...as I said each state is different..on what is customary BUT you can write anything you want in a contract so find out what is normal for your area..example:
In Iowa the seller splits the cost of title insurance, pays for the revenue tax on the deed, prorates taxes and usually has a closing fee to the title company, real estate company and of course the sale comission.
In Missouri the seller doesn't pay any of the title costs, does prorate taxes, no revenue stamps here, pays the title company and commission.
As to loan closing costs..Some sellers will pay some closing costs in rare instance but it is usually a set amount like..Seller will contribute up to $x,xxx.xx toward buyers closing costs. Make sure you state however that if the costs do not total this then the remaining go back to you. Normal closing costs for a buyer would be about $600-$1200 not including points, origination fees, and prepaid expenses like escrow deposits and first years insurance. maybe a bit higher as Title insurace is a dollar amount per $1000 calculation $3-4K is very high.
For a qualified buyer there is no reason for you to pay part of thier costs unless you have a difficult home to sell or you have a first time buyer that is short of cash but then factor in what you will pay into your counter offer. Also don't let the buyers broker or bank tell you what you are going to do, they don't represent you and have no contract with you.
Again..don't sign any contract until you fully understand it and if you don't get a local attorney that is well versed in real estate to tell you what it says. Not all attorneys are well versed so make sure they understand the current laws and customs.