Idea for speeding up transactions

I have noticed that getting shipping information and then calculating shipping costs adds a couple of emails to the transaction. This can even add a couple of days if the buyer lives several time zones away.

But If on the member lookup someones zip code was included in that information you could calculate shipping costs right away and send it back with your first reply to the buyer.

Sometimes you can look at their current ads and get it from there but if they dont have an ad posted you cant use this.

What do you think of this idea?
It's a good idea. What I do is estimate using my scales at home and the UPS/FedEX website. I try to be conservative in my estimate. If the actual cost is less, then I reimburse. This is very easy if you use PayPal. I know some don't like to use PayPal, but I've nothing but positive experiences with them and find it to be the best way to deal with payments.
I too love paypal. Once a buyer or seller agrees to this, the rest is simple.I think any sale or purchace should be open to some barganing re. PP fees or shipping charges. Some will give you a hard time on these items. One thing I get a big kick out of : "OBO" will appear in the add, and the seller wants a little blood along with/ once they know you really want the item. The exchange of zips, is of less signifcance; once the price and fees are settled.
When buying I don't make a big deal of shipping costs as quoted by the seller unless is seems silly.

I spend more time on packaging and method of shipping. Still, your suggestions do make it easy to check on pricing.