It depends on how badly you want the house.
From the seller's perspective, it is not their problem as it is your lender telling you that it has to be done. If it is a Buyer9;s market, they might prefer to pay for the work so that they don't lose you as the buyer. In a Seller's market, they will probably decline to pay for the changes, as they can probably find another buyer who won't have this issue (cash buyer) or is willing to pay for it.
From the buyer's perspective, this is an added expense you didn't count on (Welcome to home ownership!) and you probably think the seller should pay for it or reduce their price so you can pay for it. However, it is all negotiable. Check the language of the contract, usually inability to obtain financing is a clause which would let you back our of the deal without penalty.
1),Seller might pay (means he makes less $)
2) Buyer might opt to pay, in order to obtain financing (essentially, the house just cost more)
3) You agree to walk away from the deal & both parties start over with new partners.