Just don't make the expectations so high that you set them up for failure. Each staffer should submit a personal inventory of their strengths and weaknesses related to working the exhibit. Some are good at presenting the company story, and others are exceptional at capturing lead information. This will increase your chances of success since the staff will be working from their strengths. Expect to work hard.
Trade shows are hard work.
Booth staffing involves standing for hours, engaging strangers in endless conversation, and presenting a message over and over again. Sales personnel are not afraid to work hard. They thrive on it. It is the unknown that creates the discomfort and the lack of enthusiasm in working a trade show. Let them know that you know it is hard work.