Weird shoe sizing

What is going on with your shoe sizes?? I have been a size 5 for as long as I can remember. Now I'm taking 4s in your store only. I bought shoes for a friend. She is a 6. They didnt fit and were too big. I swapped them for a 5. They are STILL too big. Now I'm hunting for a size 4. This is crazy. What's going on with your sizing. Something has changed, and for the worse.