I've only had one bad transaction as a buyer, but it was a whopper ... I have over $800 tied up in bankruptcy court over it. The gentleman's feedback was great, and promptly started to go south almost at the moment that I purchased the item from him. He couldn't deliver, and started a repayment plan. I got about a quarter of my money back from him before the bankruptcy letter came. You can still lose out even if you do due diligence.
As far as selling goes I give people a lot of slack because most (99%) are honest people and the few % that are late usually have a very good reason, and understanding and compassion goes a long way here.
Also, with regard to pricing on eBay, I have an article that might be of interest to you all on my website:
http://www.mightybargainhunter.com/priceitonebay.htm
John