I used TheMilesBroker 2 days ago. I added an Authorized User to my account, and transferred 52k MR points his ANA account. Received $598 for them. 1.15c each in increments of 1,000. Was easy, just had to make 2 calls to customer service. One to add the user. Two for expediting the user on the MR transfer. They were able to do it without a problem. I sent a screenshot of the MR history, showing the transfer and he sent me the money via Paypal.
If you provide the broker with the above requested info, 4 on the front, 3 on the back, account password...etc. I think he can add the Authorized User and transfer the points out. Saving him having to explain to you how to do it... But, I agree, that is a lot to ask. I wouldn't feel comfortable doing that.
There is a bonus of 10,000 miles if you sign up for the "Pay Over Time" program. You don't have to use the program, but it turns the card into a credit like card, as the balance can be paid over time. Free 10k MR points ($115 @ quoted rate).
ALSO, flights to/from USA/Japan on ANA start at 40k miles... A great value since they are $1600+.