It depends. If your customer is simply leasing out the space to the virtual currency kiosk owner/operator and collecting “rent” payments, the owner of the kiosk is the MSB, not your customer. The owners of the kiosk are required to register with FinCEN as an MSB. Your due diligence on your customer would be to collect a copy of the lease agreement between your customer and the kiosk operator for your Enhanced Due Diligence (EDD) file and document if the monthly rent payments seem reasonable.
If your customer owns and operates the machine, then they would be considered an MSB and you would need to collect relevant due diligence such as FinCEN registration, BSA Policy, and evidence of their most recent BSA Audit/Exam. Significant monitoring to understand the flow of funds and how the customer identifies and monitors the users of the machine would be needed.