Is it permissible to sell shoes that contain a small percentage of pigskin (the leather lining the inside of the shoe directly touching the foot)?

Scholars have differed regarding the purity of animal skins – including pigskin – after tanning. The correct view is likely that they become pure through tanning, based on the hadith narrated by Ibn Abbas (may Allah be pleased with them both): "When the hide is tanned, it becomes pure." Accordingly, there is no harm in selling or using the aforementioned shoes.