Have you ever called a store to find out if they're open? When they pick up the phone and say Hello, it's hard to ask "Are you open?" since it's now SO likely that they are. So here's what to say when they answer the phone:
"How late will you be open?"
That's the no-embarrassment question. And it even allows them to say, "Actually, we're closed," if they're just there to do inventory.