Finishing sauce to me I guess is something the individual puts on themselves. I put a little rub and vinegar sauce in my pulled pork before I serve. Not much, just enough to give a hint. Actually what I do is this. After it's pulled, I put a whole bunch in a frying pan. I mix my vinegar sauce with water, 3 parts water to one part sauce, enough to cover, and a little rub. Then I cook it down until I just barely get a little water over the spatula when I press down on it. I then serve several sauces on the side. My vinegar sauce (not watered down), a sweet sauce and a spicy KC sauce. I let them choose what sauce, if any, they want to use. I generally use a bit more vinegar sauce ( a little dab will do ya) or none at all.
Another good finish is to pile coleslaw on top of that sandwich. I prefer a vinegar based, but mayo based will do ya jus fine if that's what ya like!