5 Invaluable Sales Tips From a Former Door-to-Door Salesman Knocking on somebody's front door is the coldest call there is.

When I tell people that I was a door-to-door salesman -- yes, in this century -- some are shocked. They didn't even know that kind of work still exists.

Granted, it's rare. But it's the best sales education I could have received. Knocking on doors to sell books taught me invaluable lessons that apply to every form of sales. There's no question these lessons helped me co-found a successful tech startup, Pipedrive.

Here are five tips I learned the hard way.

1. Get to "no" faster.

You will be rejected. Often. There's no way around that. No one has a 100% close ratio. When I was knocking on doors, one person called the police on me. Others told me to "get the [expletive] out." A colleague once had a guy come to the door with a gun.

But most people are too polite. They let you make your pitch even if they have no interest in buying. And that's a problem of its own. Time is your most important resource. But at first, you tend to waste it by staying too long with people who aren't going to buy. I made this mistake.

Related: 4 Sales Strategies to Increase Your Average B2B Deal Sizes

Then I learned to set a rule for myself: No more than 20 minutes at any house.

A crucial way to make this happen is to help people feel comfortable saying no. I'd chat with the prospect first. Then, before offering a demonstration of the books I was selling, I'd say, "I think I understand what your problems are, and how this can help. I'll show you what I have here, and you just let me know whether it's something that might help you, or something that doesn't."

That way, customers are less likely to hold off on saying "no" out of politeness. But there's also another benefit: They're more willing to take a serious look at the product once you've made them feel comfortable saying no.

2. Get out of your head so you can read the signs.

To get a sense of whether someone is a serious prospective buyer, you need to learn the subtle cues they're giving you. To do that, you have to first get out of your head. I couldn't read the signs when I was anxious. At first, I was so focused on what to say next that I missed what was right in front of me. When I let go of that anxiety, everything changed.

The key is to know your craft and your pitch so well that you don't have to think about it. It's almost like pressing "play" on a tape player in your mind. While offering your spiel, you're studying the prospect. You see their facial expressions. Are they looking at you? Do they seem comfortable? You read their body language. Are they looking for a chance to close the door politely? Are they nodding along to what you're saying but not really focused on it?

Related: 7 Psychological Strategies for Mastering Sales Negotiations

All of this applies just as much to detecting people's vocal nuances over the phone. After a while, you learn to hear the truth in people's voices just as you can learn to see it in their eyes.

3. Don't try to convince.

This seems counterintuitive, but it's essential. If you go into sales thinking that you need to "make" people buy, you'll fail. Unless you're a cute little kid selling cookies in the street for a dollar, pressure isn't going to work. People see what you're doing, they don't trust you, and they don't believe what you're telling them.

Instead, get to know people. Your mission is to understand them. What are they going through? What are their ambitions and needs? Focus on them, first and foremost. The product comes second.

Once you understand their story, you can connect the dots for them. You can show them how what you're selling can genuinely help solve their challenges and make their lives easier.

Also, the more you get to know individual prospects, the clearer sense you'll get of the types of customer who are more likely to buy your product – and the kind of pitch they each need.

Related: 5 Strategies for Entrepreneurs to Improve Sales

The books I was selling were for parents to help children with subjects in school. I learned to gauge an entire street in advance to get a sense of how many families with kids likely lived there. And I learned to tell from the height of a basketball hoop what age the children likely were, so I could tailor my pitch for parents of elementary school kids, middle schoolers or high schoolers.

4. Be gracefully direct about next steps.

If someone is seriously considering a buy, you need to get structured about making it happen. This requires finesse. A prospect might need to bring the offer to others at his or her organization, or discuss it with the CEO. So they might say, "Let us think about it internally and then get back to you."

Don't leave it there. Selling door-to-door, I learned that they key is to ask new questions out of sincere interest -- not out of pushiness. I might say, "Sure, absolutely. If you don't mind me asking: What is it that you want to think about most?" Potential buyers respond well to curious people.

I also asked early in the conversation whether the person I was speaking with would generally make this kind of purchase decision alone or with a spouse. If it were the latter, I'd save time and come back later to demonstrate the product.

This same idea applies to phone calls. Feel free to ask a prospect early on who else may need to weigh in. At the end of a call, ask: "When do you see yourself talking about it internally and when could we connect again?" Be as specific as possible about the agreed next step.

5. Don't string yourself along.

Sometimes, prospects are only claiming they need to think about it or discuss it with other people. They've already decided not to buy, and just don't want to break your spirit -- at least not to your face.

So how do you stop the cycle of endless calls to see whether they've decided?

Change the question. Don't ask people simply whether they have a decision. Instead, ask: "Can you see yourself making this purchase within the next month?"

A colleague of mine in door-to-door sales finally made this change, and the vast majority of those he called finally said "no." It was a painful realization for him, but a crucial lesson. His time was better spent back out on the streets, knocking on new doors.

All of these tips will be easier to pull off as you build your confidence. Ultimately, confidence will be your strongest asset. One of the best examples I've seen was how my colleague met his wife. When he asked her on a date, he said, "I'd really like to go out with you. A couple of friends and I are going to have a party on Friday, I'd love for you to come, but I also understand if you can't make it -- that's fine too." He created a comfortable environment for her to accept or decline.

Later on, she said that confidence made him stand out. It even made him a bit mysterious. She felt a pull to go see who he was. He was direct, honest, interested in her, and graceful. Never pushy. And ultimately, he "sold" himself to her.

So take these lessons to heart to use in your career. And don't be surprised if they also pay off in the rest of your life.