Is the plan turning that slave merchant into slave himself?
I sort of wish someone would follow through on this, but JP authors fetishize it too much.
It's like stealing something from someone, then trying to claim ownership and selling it back to them.
All that it would result in is getting knifed in the back. Without force behind it, it's simple kidnapping.
"Hey, you kidnapped and enslaved people unwillingly? Cool, I can do that too! Surprise, I own you now!"
I wish authors would think the universe through a little bit first.
Generally all their contrivances for "isekai society" collapse into warlord rule.
Edit: I wish this author would consider their own universe's rules, and try to be consistent if it's "a legitimate profession":
"By the way, did you know your slave was illegally kidnapped?" (Possession of stolen/illegal property)
"Oh shit, she never remembered. How can you prove it?" (Debtors trying to avoid the repo man)
"Here's a truth spell administered by the church." (Here's the 2-month verifiable guild/kingdom/police report)
"Oh crap, this is terrible for business. My guild license could be revoked. We'll undo it at the slavers guild ASAP."
That would be the only way any of this author's "slave trader profession" universe could possibly make any sense.
Otherwise you could kidnap people off the street left and right.
Or open up the "slaver city" for
*(looting competitor kingdom) punitive force.