I'd argue that it's a lack of professionalism that's the real problem. It's easy to negotiate yourself out of a perfectly good job offer if you don't know what you're doing. And lets be honest, most devs haven't the slightest clue how to do salary negotiations. Someone posted Patrick's guide, and that's a good start, but you need to learn a whole bunch of little lessons about the corporate world before you can really start to apply them effectively.

Until then, why not just work for market rate or just slightly below? Don't stress yourself out, there's no reason to and it'll hurt your bargaining position. 90% of it is done before you even get to the table anyway.

It doesn't matter how much value you create for your employer; it is how many other people around can create the same value for your employer.