A markup of the contract means "counteroffer" by the other party. It is not final!
Here is the definition
A real estate contract can be drawn up by both sides collectively and signed, or composed by one side, signed, and offered to the other side for an agreement and signature. Counter offers may be made before the contract is signed by either side. Each additional counter offer, often accompanied by a mark up of the contract, must be initialed if made after signing.