I always talk directly to the Kitchen Manager or Chef and then fill in the Wait Staff. Some tips: If getting grilled food, ask if they use seasonings and/or sauces on the grill. Check if gluten free. Some Chefs have offered to clean a portion of the grill while others may offer to grill on tin foil. Always ask for baked potatoes un-cut with butter, etc. on the side (you don't want someone grabbing any knife and cutting your potato). Check drinks for any mixes used to make the drink.
If you want to know what it really is like to be celiac....check your medications and suppliments for gluten. Buy a new toaster. Buy new pans if teflon is scratched. Throw away any wooden spoons/cutting boards. Buy a new strainer. Buy new plastic food storage products. If it is pourous or scratched...it must go. Vacuume out all your cupboards and wash them. Same with pantry. These are just some of the things celiac's deal with on a regular basis. It is very difficult to trust your food prep to someone other than yourself. This is why many celiacs do not dine out often and is why a third degree questioning is necessary and why it is necessary for staff to take you seriously, regardless of the fad dieters out there.