I have several hints from my experience with EBay.
Here's one for the sellers. If you know you are having problems with your email, make sure to convey that to whoever wins the bid on your item. I won an item one time (the only time I've won), and the person had made sure to put a notice on the page that they'd been having problems with people trying to contact them. So, they gave an alternate method of contacting them. Turns out, I was able to get through. But, it was very helpful to know that they had tried to do everything possible to make sure I'd be able to if the email didn't work.
Also, I have to say that I had a wonderful seller. I had purchased some pictures. The seller and I corresponded several times before the transaction was totally complete. In her emails, she gave me a lot of background on the pictures. They were from a tv show reunion that she'd been to. This person told me stories of the people - where they were now, what they were really like in person, etc. It was nice to get to know my seller a bit more personally. If the opportunity arises, try to be as friendly as possible. Really helps your rating if the buyer feels like they've got a trustworthy friend in you.
And, I'm going to reiterate Katie's advice that you MUST leave feedback. It's important that you give feedback - whether you are the buyer or the seller. That information is very helpful and is necessary to get a person's rating established. The only thing that I felt a bit frustrated with in my experience was having to beg my seller to do feedback on me. I had to send several emails before they would. And, that wasn't fair.
[ 11-27-2001: Message edited by: Linda1 ]