Questions for hiring a credentialing specialist

Hi Everyone,

I am a manager at an Orthopedic facility in CA and we are interviewing to hire a credentialing specialist for our practice, can you all please recommend any questions I should ask to judge for knowledge about credentialing and setting up ERA, EDI and EFTs that would give me an idea of the person's knowledge.

Also in your practice do you have a person dedicated to this and working 40 hours a week, since the last guy we had was billing 40 hours a week doing credentialing for 3 MDs and 2 PAs. But a lot of the people I talked to suggested that credentialing is not that much work and I should consider the fee for service then a salaried employee, what do you guys think.

Thanks in advance.