It's not just guns and drugs that are up for sale on deep web sites.
Vendors also list guides on how to commit other illegal activities.
There's lots of reasons someone might want to dig up dirt on someone.
Maybe you're going on a blind date, need to rent out a room, or are hiring someone new to your small business. I've warned you many times that all that fun stuff you're putting up on Facebook is letting out in public information that perhaps should remain private.
The guide isn't available for free, in fact, it was being sold for Bitcoins on a deep web marketplace.