The difference between blank labels on Avery.com and labels bought in store is that the labels bought in store have a more limited variety as they are pre-packaged. Blank Labels purchased on avery.com give you the ability to choose the size, shape and material you want as they are custom cut for you. You can also order blank labels in any quantity.
See the Avery Blank Labels:
https://www.avery.com/category/shape/all/
See the Avery Retail Packaged Labels:
https://www.avery.com/products/labels/usage/all-labels