There are about 6 distinct styles of BBQ sauce in the Carolinas in 3 major categories. Tomato based, vinegar based and mustard based.
In the upstate of South Carolina we prefer the mustard based. Mustard thinned with a bit of vinegar and some sweetness added with honey or molasses and whole lot of black pepper. If you really want to do it right, puree a peach for the sweet part.
You know its right when you buddy takes a bite and just nods and mumbles "damn!" while chewing a mouth full.