I used to have the same kinds of reactions that many of you are talking about here - I would get one whiff and get a major migraine. There are masks that you can wear. If shop owners are doing something to increase allergy problems - ex. potpourri, burning insense - sometimes they get the message. I don't have problems in fabric stores any more. I severely limit my time in shops that have strong smells of potpourri, candles and things like that. The worst store I have been in lately is Bed Bath and Beyond. I really like to look there, but I won't be going in again unless I have a mask with me. I have even said something to them, however, one customer having a problem is one thing, several/many people complaining may have some impact. I hate air freshners, perfumed detergents and conditioners, etc.
I have found that unless someone has had problems themselves or knows someone who has problems like this, they just plain and flat don't get it.