Everywhere we turn these days, online and off, we're being sold. It's a din of sales messages.

For business owners, everywhere you look there's another course or Webinar or blog you should read that aims to teach you how to sell better. But after watching a preview copy of this week's upcoming Shark Tank episode, I wonder if entrepreneurs might do better to learn one overlooked skill: When to stop selling and close the deal.

On this Friday's episode, one of the entrepreneurs blows a chance to have Shark Mark Cuban invest in his business. (You'll have to tune in to…