Last Wednesday I offered some thoughts regarding verifier independence and perhaps wasn't clear. Simply because a firm does a client's audit shouldn't preclude them from taking on the verification. Independence needs to be reviewed regarding the full breadth of the services offered. As for the case I cited (about an accounting firm not taking on a client's verification), while I don't have any specifics it most likely was done because they were already doing a great deal of work for the client and felt that the additional task might be problematic.
No question that the subject of independence is a difficult one. What might be clearly a conflict in one person's eyes might not be in another: this is one reason that the determination of independence is to be done by the verifier and client.