In my anecdotal experience of reacting to “wow this espresso is good” it’s often been a Slayer machine. It’s been a rough indicator of where to get good coffee for me.

I tend to look at the grinder and also the choice of the beans (roast level, consistency, chips). As another commenter pointed out you do occasionally get places that will buy a super fancy machine but have no idea what to do with it. It's rarer to spend loads on a fancy grinder if you don't know what you're doing.

La Marzocco has such brand recognition that a lot of newbie coffee shops would buy one, but people who buy a more niche commercial machine like a Slayer or a Synesso probably know what they are doing. Still, there's nothing wrong with the machine itself and there are plenty of really great coffee shops with a La Marzocco.