I wouldn't trust them. If it was me I'd tell them to keep a rack empty and that you will drive it until it is heated to operating temperature and then return to the dealership to be put on the rack and so that they can DEMONSTRATE to you that the transmission fluid level is proper. Why? Because there is no way to assure a proper trans fluid level when it's filled cold, and that is exactly what they're going to do. Don't take no for an answer. And while you're at it, you might inquire rather pointedly about the mystical three dipsticks and whether they have installed the proper one. (Hint: If it isn't on the bill, they didn't do it.)