I have an ironclad rule when it comes to hiring salespeople: Never, ever hire from a competitor. Like most of what I know, I learned this rule by making mistakes. Fortunately, I made them early on, in my first startup.

I had the usual reasons for hiring my competitors' salespeople. I figured they would save me time and money. After all, they already knew the business--in this case, messenger delivery--and so I wouldn't have to train them. They could be productive from Day One. Of course, I was also hoping they might bring some customers and leads with them, allowing my company to grow faster than it would if I hired salespeople with no experience in the industry. It seemed like a no-brainer. What could go wrong? As it turned out, plenty.

To begin with, they brought with them a lot of bad habits I could never get them to change. They thought they knew more than I did about selling our service and wouldn't listen when I told them how I wanted them to do it.

Among other things, they were constantly going for the quick sale. They ignored the price guidelines I set and made promises I would never have approved. To top it off, they weren't such great salespeople. The people I brought in from outside the industry and trained myself regularly had better results. I realized my competitors had good reasons for letting their ex-salespeople get away.

Yes, it takes time to train your own salespeople, and you'll wait longer for results. But I've learned there are no shortcuts. If you build your business to last forever, you'll wind up with a better, more valuable company.

From the May 2014 issue of Inc. magazine