Batch consistency is the part nobody warns you about. One photo with a clean white background looks fine; ten photos where nine are #FFFFFF and one is #F7F7F7 look broken on a grid.

Three things that fixed this for me:

1. Pick one target value and check it, not "white". #FFFFFF is 255/255/255. Sample five points with the eyedropper - corners, centre, both edges. If the edges read 250-252 you have a soft falloff, not a flat fill.

2. Normalise the export, not the source. Resize and compress last, and use one setting for the whole set. A JPEG at q85 can drift flat white to 253 while an adjacent PNG stays 255, and the seam shows in a carousel.

3. Watch shadows. A soft grey drop shadow under the product is correct; a grey cast across the whole frame is not. Keep the shadow under the object and the rest at target.

Full disclosure: CleanWhiteBG is my product (https://cleanwhitebg.com) - free, no signup, white-background replacement. Weigh the tip accordingly.