Closing costs can jump 40% because they do not like the look of your face that morning, chances are that is why it has skyrocketed. They can also base it off of your payment histories with every single vendor you have ever used, miss a power bill payment, that can add a half percent to closing, it is really their own little game of make it up as they go.
I'm not sure what you mean by this? I can't remember a whole lot at closing (aside from down payment) that was based on my payment histories or whatever, and I just closed on a sale of a home last month. I recall it being commissions, county and FHA fees, inspection costs, and fees to the title/abstract company.
My Realtor (a good one) estimated them off the top of her head - within a hundred buck or so - the moment I told her verbally what I realistically expected to get for the house.