This is really important. I love programming and am somewhat introverted, but being newlywed with a wife who couldn't work (visa), a mortgage, and a commission plan really made me learn to sell. The really good salespeople aren't deceptive, and I luckily learned from them.

Also: if you're at a good company the engineers don't scorn the sales people (instead: "you guys bring in the money that pays our salaries") and the sales folks actually sell the product to people who will benefit from it.