Many years ago a friend of mine bought 500 leather hats from a manufacturer in India, at a ridiculously low price. When they arrived at his shop, they were nested one inside the next, in lots of 50, and shrink-wrapped. When he opened the packaging the smell was appalling - they had obviously been tanned using a process that involved doggie-doo!
He moved them all to a small spare room, threw in a handful of lavatory cleaning blocks, and taped up the door. The last I heard, he was opening the door every six months to throw in more lavatory blocks, and resealing the door! Don't know whether he ever sold them. . . .
Since then, I have learned that in some parts of India, small boys and girls are employed to collect what dogs (and pigeons) leave behind, for use in the tanning process.
Another friend's father worked for a removals company during the 1930s, and if they had a removal to London, they would call at Battersea Dogs' Home on the way back and collect drums of 'pure' (that's what it's called!), and sell them to tanneries in their home town. Where there's muck, there's money!