You might be surprised at how many salespeople are also introverts. Through years of being an (introverted) sales engineer, I've learned that outgoing socialization can be tough even for salespeople. Some of the most successful sales people I've worked with need to go quietly recharge for a day after a ton of meetings, just like I do. The biggest differentiator there is that the ones who can't manage it with a smile don't last long.

Relationship building in sales, like all skills, can be learned, even if it's draining.