You're pitching your product at a trade show and you have just completed a brief spiel to a small group of potential customers in your booth. Two members of your audience walk away.

That may be good.

But one of the remaining prospects is really taken by your pitch. He doesn't just hear you out, he lingers, pumping you for details, asking about old products, chatting about business.

That's not so good.

On the trade show floor, familiar selling caveats are out. Limited time, not patience, is the main factor. The goal is to identify potential customers as quickly and conclusively as possible, to eliminate abruptly anyone who is not a prospective buyer, and to capture swiftly, on a lead card, all the information necessary for contacting a likely client once the show ends.

"It's better to sell the next step in a sales cycle than to sell the product," counsels Diane Weintraub, director of marketing and communications at Timeplex Inc. in Woodcliff Lake, N.J., a company that uses trade shows extensively in the marketing of its data communications products. "The idea is to keep the traffic flow going, and not to buttonhole one guy for an hour.

"Assume, for instance, that the attendance analysis we look at before a given show indicates that we can expect 15 customers to pass by our booth every hour. Our sales staff can handle 8 customers an hour. That means they've got to make some quick decisions about who's out, who's in. They've got to qualify and qualify and qualify."

"Qualifying" is the process of determining whether a visitor to the booth is a serious sales prospect or a mere tire-kicker. The quicker the booth staff can qualify prospects, the more effective it is. The more nonprospects they get rid of, the better they are doing.

That approach, of course, goes against the grain of most selling. Thus, many companies that use trade show marketing have found it necessary to untrain their top field sales staffers and retrain them in trade show selling. Infocom Inc., for example, a Cambridge, Mass., software company, had its booth staffers put through a daylong workshop in preparation for their first trade show -- the Softcon show in New Orleans this spring.

"You have a great booth, a great product, and a great opportunity," Admore Inc. trade show consultant and executive vice-president Robert Francisco told the 20 Infocom employees. "But all that's mere fluff if you don't sell effectively."

Francisco hammered home the differences between normal sales techniques and trade show selling, outlining the roles that each staff member would play on the floor and detailing, step by step, the method for moving a visitor from early qualification into the booth for further information-gathering, and then briskly but gracefully back to the aisle.

Training salespeople for trade shows is no easy task, says Charyn Ofstie, a Chicago-based trade show consultant who has run dozens of such sessions. "You're up against egos," she explains, "often working with highly skilled salespeople who have to unlearn some instinctive habits.

"The whole point of a trade show is the chance to meet head-on," she says. "We role-play being out there, up front, making eye contact. We define specific actions, dialogue. Otherwise, a sales rep at a trade show is like an actor thrust out on the stage before he's learned his lines."