Claims to be a debt collector wanting to "help us collect on some debt we might have outstanding", from customers.

Yeah, we don't have anyone who has any checks which haven't cleared for us, nor have we contacted anyone concerning trying to collect for us. Plus, the CID doesn't match what I've found online for the phone number, and the callback number left was not the same area code as the call supposedly originated from, so I'm assuming probable scam at this point.