If there are books with shoe prints on them, I think it's more likely that the packing people at the printers did it. The books would have been shipped to Amazon from the printer. I can see Amazon employees not noticing the damage or not caring.
Vaseline on the books doesn't make sense to me. As I said earlier, the packers would't have time to do it, and if the books had been greased up earlier, it would have been reported because of the problem of transfer to other products and getting it on the conveyer belt.
Well as an author, having your book on Amazon is important. They are now considered the largest book retailer around.
In many cases the “publisher” really isn’t sending actual books to Amazon either. They send a digital copy which is then either available on Kindle or Amazon prints copies as they are sold. So it is possible the damage is happening at Amazon itself.