Hello everybody,
I recently saw a copy a book which featured a bookplate signed by Chistopher Tolkien. I asked the seller a proof of authenticity, he told me he has a letter that can't show cause it contains private information.

Since I am relatively new to collecting Tolkien items, I just wanted to post here to get some thoughts from you. What would you do in this case? Also, is a book with a signature applied via bookplate valuable as one which was directly signed?

Thanks in advance.