Yeah, the first 100 applicants are going to be people from World Financial Group.
Every caller will be screened by me before they get to an old person. That is step one in fraud protection - open to advice here!
Do you have more steps? "Open to advice" is a bad approach to ethics. Perhaps hire a consultant?
Screening volunteers to deal with the elderly is a fairly standard process for hospitals and care homes. Maybe interview a few of them on how they do it?
I think they do it by running background checks and meeting the job applicant in person. That wouldn't work very well for remote-only work that recruits people from anywhere. I don't see how you could vet people with anything approaching due diligence without eating up most of your first few months worth of fees up front.