First of all, if there's no transaction you can't get bad feedback. There need to be an actual purchase (money changing hands, not just interest) or trade (items bought or sent), something along those lines, from what I understand. You can't leave feedback for someone because you wanted to buy something and didn't get back to the seller fast enough or it was to someone else.
I think a week is way too long to wait, especially if they haven't even agreed to the price. A lot of buyers everywhere vanish all the time. In my experience its the most common after you name your price. I agree that 24-48 hours is more than enough time to decide if a price is okay, but that's your choice.
I'm glad they got back to you! Hopefully the rest of the sale goes off without a hitch :)