Adding to that, even if you don't like negotiating, it's helpful to understand the tactics used by the other person so you can counter them (or at least be aware of it).
For instance, my favorite tactic when someone is pushing hard to sell me something or negotiate is the "Appeal to the authority" (i.e. "Let me first talk about it to my wife (or co-founder) about it."
Another popular negotiation tactic is to get asked between option A or option B, where in fact you could simply respond with "option C is more what I'm looking for".