Sharpening finds edges and makes the light side lighter and the dark side darker. Editors control it with an amount, a radius and a threshold. A small radius brings out a weave or a stitch line; a large one draws a visible outline around the whole product. Cameras and phones already sharpen their JPEGs, so further sharpening of a phone photo adds to what is there and quickly overshoots.
Sharpening belongs at the end, once, at the final size. Shrinking an image after sharpening can make fine knits and stripes shimmer with false patterns, and enlarging it enlarges the halos. On a white background an overdone edge shows as a dark rim around the product, which reads like a careless cut-out. Viewing the result at full size, one image pixel per screen pixel, shows halos that a reduced preview hides.
A blurred photo stays blurred. Sharpening raises the contrast of the edges that exist; it cannot rebuild detail lost to missed focus or camera shake, and on dark fabric it mostly sharpens noise. Several marketplaces turn away blurry images. The remedy is at capture: a steady support, more light, a faster shutter and focus set on the front of the product.