This answer refers to Philadelphia, PA.
Buyer' s Closing Costs, include Mortgage Fees, Transfer Taxes, Title Insurance costs, Home Owner's Insurance. Some mortgage fees are negotiable, and mortgage points can be paid for a lower interest rate. Transfer Taxes are usually divided equally between the buyer and seller, but it is not necessarily so. Most of the other fees are not negotiable.
Who pays the buyer's closing costs, buyer or seller, is negotiable up to a % which is allowed by the buyer's lender, usually 2-6% of the purchase price. Commissions are closing costs that are usually charged to the seller, but a different arrangement is possible.
In an all cash transaction any and all closing costs can be paid by either party.