Some buyers make offers including a condition that the seller pay all or some of the closing costs.

Some sellers offer the incentive of seller-paid closing costs to try to entice buyers.

What's really going on here?  There are a few ways to look at it:

• For some buyers, it can make all the difference in the world!  Some buyers are pursuing 100% financing (which is getting harder), and may not even have funds to pay their closing costs.  For these buyers, if the seller won't pay the closing costs, the deal won't happen.
• For most sellers, it doesn't make a bit of difference!  Paying a buyer's closing costs changes the net proceeds to the seller -- but the amount of the closing cost allowance simply becomes another term of the negotiations.  The seller subtracts the closing cost allowance out of the contract price, and negotiates accordingly towards their desired net proceeds.