Forget for the moment whether you believe shyness can be "cured" (it's not an illness, it's a genetic trait, you have those cave people who rushed out to confront the sabre tooth tiger and those who hung back to gather the nuts and berries in the fields and become the story teller around the campfire, etc.) do you wish you could be more outgoing and less anxious around people? Most of that has to do with experience and working at it and it could be your shoe store is a great place to do that as it is "smaller" than a department or big box store, for example? Shoe stores don't usually have huge hoards of people in there at once and that kind of pressure so you can learn to approach people one-on-one.

Make a list of things you can try? I would start with just smiling at a customer as you are walking by and saying, "Can I help you with anything?" Most are going to be "just looking" and/or some will look/seem less threatening if you think about it; pretend you are on a park bench or at a Starbucks watching people and trying to figure out how old they are, what they do for a living (based on time of day? Are they on lunch break or stay-at-home-moms, did they come in with anyone else), whether they're single or married, etc. Be curious about them and you may not remember quite how anxious you are.

Think of the shoe store as only a school/practice ground rather than that you are stuck in retail. Yes, retail is depressing to me too but I think about the bigger picture; it is a store/business so has all the parts of business: administration, personnel, accounting, customer service, sales, transportation, product & product development (they make "new" styles depending on what sells), advertising, etc. See if you can figure out how the store does those things and which seem more interesting to you. I took an accounting course in my 40s because it was the only part of business I had never worked in and it turned out I was really good at it and really liked it. Make yourself a little plan on how you can move from a shoe store to a larger store with a department you want to explore. When I worked for Sears Roebuck right out of school, I was put in the credit department but did horribly because my job was to call the people who did not get approved for credit and tell them why! I could not do that (I understand your fear). They moved me to the customer service department and that was calling customers to tell them when their stuff was scheduled to be delivered (happy) or that it was out-of-stock and there would be a delay (which could get one literally cussed out and management listened in to our phone calls) but I was not alone, there were other girls my age who helped me become less shy and who I could "copy" what they said, etc.