I once received a job offer, the superintendent told me what the "current" salary would be, but he also said that he could work some numbers and come up with more if necessary, and then said, "What will it take to get you to come here?" Never been asked that before. I didn't want to sound greedy, BUT, he did ask, and I knew that another $2500 in the salary would help when it came to rent. So I said, "could you add $2500 to the deal?" I could hear him doing some pencil work and he said, "Let me get back to you."

Never heard from him again.

With that said, if they have offered you X, and you think you can get Y....if they agree to give you Y, then you probably should sign the contract.