dramaqueen, I have had relatively few experiences with genuinely hostile customers (presales or actual paying customers). I've seen many more frustrated people than actively hostile folks. I'm also fortunate enough to have a psych major on support staff, though; so whenever something's been questionable and I'm not sure of my own conclusions, I ask Apryl for a second opinion.
How many hostile customers you attract can depend on a lot of things: your site's design, the general impression of your company, your staff's attitude (poor initial communication can turn a frustrated, aggravated person into a hostile person), and an entire boatload of factors outside your control. I wish it was possible to simply say, "If you have X type of plans, or use Y color in your site, or say Z, you'll probably be more attractive to hostile shoppers." Then we could all just stop using X-Y-Z, and sit back and have a beer
It's probably not possible to completely avoid the hostile folks; but it is possible to handle the situation in such a way that they can't really continue to get wound up without appearing incredibly, blatantly in the wrong. The trick is to learn how to spot hostile customers, and learn how to immediately stand firm without being defensive.
Spoken and written communication classes are extremely valuable in learning how to modify your own communication style, as well as identifying truly hostile communications.