Hi Sharon,
I m sorry to hear that you had such a bad experience with an independent shops, especially as a lot of independent running stores tend to be very good in the customer service and offerings, it is what makes them different from many chain stores. Independent store strive on customer feedback and recommendations, and any store which behaves as you described above should get slammed for behaving in such a negative fashion.
I run a sports specialist myself, and consumer law entitled you to a full refund within 2weeks of date of purchase if the product is unused and in its original packackaging, with original receipt. If shops have a sign up stating that they are only give credit notes or exchanges they are in actual fact breaking the law. The reason why they have the sign up is simply because they are hoping to keep as much money in the till, and they rather you do an exchange or get a credit note, as through that they do not lose any money.
Often employees in stores will just follow what owner/manager/head office has told them, and they are often unable to do anything, however I would ask for a manager or the owner and explain your right as a consumer. If worse comes to worse you can call the police, although this is at the extreme end.
Additionally, if you slightly over pronate on one foot, and are neutral on another, you can often get away with wearing a pair of neutral running shoes, and with the right core excercises you can in the long term improve your gait. I know that when you spend 15Pounds on a gait analysis, one is always tempted to purchase a shoe from the store there, but the last thing you want to do is just purchase a shoe, just because it is a slight support shoe in your size. You need to wear the shoe that for one is correct, and simply feels right. You are the one running in it, putting the miles in, so you want the best shoe for your foot.
I know that independent shoe stores often charge for gait analysis, but in my experience a good gait analyis can be done without a treadmill and camera and shouldn't take longer than 10minutes, and for this one should not charge. And yes I m sure customers get an analysis and then buy elsewhere, but in the long term the customers that do purchase from you, outweight those who then go an buy elsewhere. Afterall, good customer service counts for a lot these days, and as seen above many shops are still struggling to provide this.