It sounds really weird, but this was a tip I had learned before, and was confirmed by an acoustician from ASC at one show. If a room is well treated, it's going to sound good inside and out. You can tell outside the room how well a room is going to sound.
Of course, if you are on the "never acoustical treatment" camp this tip won't work for you and you don't care about what I was listening to in the first place, but for those on the other team, I suggest nest time you go to a show, pay attention and see what you think.
One thing I also realized is that there are a lot of audiophiles who are perfectly happy to listen past the rooms, while I'm usually not. There are usually only a handful of rooms I can even tolerate to be in. So, depending on your listening style this tip may help you.
Best,
Erik