DD is gluten intolerant (she's working her way through FODMAP reintroductions), and we had no idea how bad she was till she cut it out, then tried some again (apologies to anyone in the ladies loos in Coventry IKEA when she was realising that gluten is not her friend
).
She's found that most places have been pretty helpful when eating out (although she only goes to places where she's researched the menus in advance), and are quite relieved when she's "just" intolerant as they can't always guarantee no cross contamination.
But, trying to combine gluten free along with all the other FODMAPs has been pretty tough, like a PP said, you'd be amazed at how many things contain onion for eg.
Gluten free is something I want to try for myself, as anecdotally it can help with fibromyalgia, I'm not sure if I should be trying the whole FODMAP thing, as some of the medical conditions in the family can be hereditary, and if I've been "poisoning" DD with broccoli and apples for the majority of her life without either of us realising, then maybe my diet has been contributing to my pain levels.
In short, it's not as simple as "only diagnosed coeliacs can be gluten free, and everyone else is a lying attention seeker faker", some of us have had GPs tell us to give it a go, and see what happens.