After years of working in corporate entertainment and production, David Spark has seen more than a few trade shows, and thousands upon thousands of trade show booths. According to Spark, the most common mistake he sees costing companies millions is booth staffers with unapproachable behavior.

In Spark’s new book, Three Feet From Seven Figures: One-on-One Engagement Techniques to Qualify More Leads at Trade Shows, he explains that each trade show attendee should be seen and treated like one of your top five best customers: a customer who over the course of their lifetime relationship with your business will easily spend over seven figures.

Because attendees see booth staffers and their behaviors first, behavior should be about non-stop engagement. Unfortunately, many staffers can’t handle the pressure of being always on, or simply don’t have the training to know how to engage potential customers.

“Your most talented and outgoing employees are your greatest asset,” Spark says, “Yet the time and money spent at trade shows and conferences is rarely focused on the people and their ability to engage.”

Although a booth’s look and design are important, they can’t create the relationships that Spark calls a “conference’s most sought-after asset. (Follow-up happens) because you made a true connection and discussed a problem or a possible opportunity.”

Here are some of the most common mistakes Spark has seen on the trade show floor, and a few helpful tips from Spark’s new book on how to help staffers get -- and keep -- attendees engaged and coming back for more.

1. They’re not approachable.

If your staffer is chatting or texting on their phone, or talking to their fellow booth employees, they won’t even be approached with questions.

“They may as well have a sign that says, ‘Don’t approach me’, or ‘I don’t want to be here',” says Spark. “They need to be the ones to create a rapport.” Your employees should be curious about everyone who walks by. They should be asking questions, not just answering them.

Related: 7 Ways to Get the Most Out of Exhibiting at a Trade Show

2. They’re too shy to meet strangers.

Each of your booth staffers should know how to strike up a conversation with anyone. If your staffers are not interested in meeting strangers and turning them into connections, they don’t belong in your booth. Spark offers conversation tips and tricks in his book, but before teaching them to your staffers, first make sure that you’ve chosen someone who is willing to try.

3. They despise rejection.

Failure is familiar to every successful entrepreneur. On the trade show floor, equating rejection with failure will immediately halt any and all progress. There will be rejection, and plenty of it. Not everyone will need or want your product. The trick is for staffers to see rejection as one more step toward finding the attendees who do.

Related: 5 Tricks to Help You Stand Out at a Trade Show

4. They don’t know how.

It the entrepreneur’s job to make sure that staffers know how to engage, follow-up and keep conversation moving. Make sure that you are giving them practical tools on how to “qualify a person for the business,” Spark explains. Do they know how to collect information afterwards? Train them how to get information for follow-up, not just a badge scan. What did they talk about? What can you use later for a personal follow-up?

5. They haven't practiced.

Even if you hire a well-qualified person who knows what they are doing, they still need to know your story and be able to sell your product like it was their own. Make time to train your new booth staffers. Have them tell you the story of your product. What is their opening line? What are the critical bits of information to push? Practice makes perfect.

6. They’re don’t realize how important they are.

First and foremost, share your mission with your staffers. Make them visualize every person walking by with the seven figure dollar sign over their head. That’s what their lifetime value could be worth. You’re going to approach them because you can help them. What does your product or service do for others, and how can it affect lives? Before they can stand behind your business with passion and sincerity, they need to know why.

Related: How to Prepare for a Trade Show Without Breaking the Bank