This happens from time to time. A lead will ask you a question and you won't know the answer. The Campaigner may not have provided you the answer.
Say something like this, "That's a great questions. I'm not 100 percent sure what the answer is, but I can make a note of you concern and pass it along. Would you like someone to follow up with you regarding the answer?"
This should open the door for a follow-up. Now this lead is a warm lead and the sales conversation the Campaigner will have with them will be much more productive.