In all honesty, after 13 years selling on eBay, I can still count on one hand all the bad buyers I've encountered. Most people calm down once you handle them with kid gloves. Just like any business, you can turn a hostile, potential enemy into a loyal customer. I humbly recommend reading Napoleon Hill's "How To Sell Your Way Through Life" for anybody thinking about a career in retail.
It's not buyers I'm upset with, it's eBay management I detest. I'm genreally not an antagonistic person but I would spit in John Donahoe's face given the chance.