We've had visitors this weekend for the holiday festivities, which gave us the perfect opportunity for some taste tests by folks that don't eat our bbq every day.
Informal taste tests are pretty good ways to test your bbq out prior to competition. You can use different spices, sauces, and techniques and ask for feedback. It works best though with folks that have eaten a lot of bbq though. You probably wouldn't receive the same quality of feedback from folks who are new to eating bbq, or who have only ever eaten "restaurant" bbq.
The true test is to try it out on folks from the "bbq belt" (i.e. southern U.S.) part of the country -- be that Florida, Georgia, the Carolina's, Virginia, Kentucky, Tennessee, Missouri, Arkansas, Texas, Mississippi, and Louisiana.