When you are making a product for a merch store, you upload an image with it. The recommended size is 1500x1500. However, when you view the live product page on the store itself, there is no way to view the image at the resolution you uploaded it in (i.e. there is no way to view the "full size" image). If you right click and open the image in a new tab, it is locked into a smaller resolution (600x600). For items that may have smaller text or logos on them, this can make it hard to see the image clearly of the product you're purchasing.