I’m a pretty good salesman, but I’m the worst negotiator. If I say, “buy my car for $10,000” and someone says “$8,000,” I’d just shrug my shoulders and say “ok”.
In fact, that happened.
Some people could be good at both. But I think it’s very hard. By definition. When you’re a salesman you want the other guy to say “yes.”
When you’re a negotiator you have to be willing to say “no”, regardless of what the other side says.
So although they aren’t total opposites, the goals are completely different. But big picture:
Negotiation is worthless. Sales is everything.