My rule of thumb is that unless I can see them preparing my food, than I do not trust what they tell me is in it. I used to work at restaurant during college and I know that we used to, well not me personally, tell people that we would do certain things for them and
not. Eg. Someone would ask that we cook wityh only egg whites and no butter while the cooks would just go ahead and add some yellows and cook it in butter. It was hard to tell sometimes if they actually did follow the customers direction.
Long story short, this is a judgement call.