Not if you're traveling. I'm making plans for a major road trip to a dog show, and a friend suggested that I go to Devils Tower. I looked at the website for that park, and dogs aren't allowed on the trails, and you aren't allowed to leave them in your car. I'm just not going to go, I'll find other attractions. But there are plenty of other times when a person might be on the road, and need to make a quick stop into a business where their dog is not, technically, allowed, and decide to push it.
And I'm going to say that I do see a difference between saying "easier to ask forgiveness than permission" if something is specifically disallowed, than if you don't know. If there's a clearly posted "no pets" sign, then you know your pet isn't supposed to be there so you're rule-breaking deliberately (as I did when I took Tess briefly into the cafe, as I mentioned earlier, although I don't know if there was a sign, I'm sure it was probably illegal. I already described why I chose to rule break in that case.) If there's no sign, then I don't think it's unreasonable to assume that it's okay, and that someone will tell you if it's not.
And they are absolutely allowed to ask you if it's a service dog. So there is no reason why they should just assume that it is, if it's not wearing a SD vest.