Depends if they always deliver or if they make a special trip for you. if delivery is part of the service than that's it, i pay and they leave, unless they are a friend, then I might smoke with them, but not cuz they're delivering, but because they're a friend.

And it's a given that the sack gets weighed, even if they are a friend, cuz business is business and I don't have money to be throwing down on a skimpy sack. If they get offended by it then that just means they're pissed cuz they can't rip you off, and they can lose my business. But then again, I can usually just call or go to someone else, some people don't have that luxury.