Make sales representatives accountable for leads. Sales representatives who receive leads from shows must be accountable for each lead. Every month there should be a written progress report on assigned leads. The information is then entered into the data base. This tracks their performance, sales made, etc., and acts as an excellent way to evaluate the return on your show investment.
Some companies use their effectiveness as part of a salesman's annual performance review.
Keeping track of your leads will allow you to measure sales directly attributable to your trade show participation.