Unable to contact previous landlords - Reject them?

I'm in the process of approving/rejecting an application for a rental. While I got a great recommendation from his current boss, where he's worked for over 15 years, I can't reach his current or previous landlords. I've left several messages and even asked the tenant to have his landlord call me. Nothing.

Reject, or have him go ahead and pay for his credit check and see what that shows?

Thanks!