A "Disappearer" sells the service of taking people and giving them new lives and identities. The Disappearer doesn't want to reveal identity to avoid being interrogated by the police or worse, tortured by criminal organisations that want to find missing persons.
Someone with this activity would have to gain trust from potential clients and be known as reliable. This means that if you knew someone that used that service, that someone was never found ever, so the disappearance worked. But logically, most people that used the service, never told anyone.
But the Disappearer could as well just kill clients and efficiently dispose bodies.
If a former client is captured several years after, and shows good health, it could prove that the Disappearer doesn't kill clients, but it would also show that the disappearance wasn't that good.
In a world like ours, how would that kind of professional build reputation, advertise and eventually be successful?