Why not?
Tiffany expert goes into antiques shop and says:
"How much is the Tiffany vase in the window?"
Dealer replies: "It's not Tiffany, it's a fake"
Tiffany expert replies "Well I think it's Tiffany"
Dealer says I wish it was but it's a modern copy.
Tffany Expert replies: "How much is it?"
Dealer says "$25".
Tiffany expert says I'll take it", and on the way out says "by the way you can find one like this in my book".
Is there a difference? Expert has given the dealer the nod that it is Tiffany. Dealer could have upped the price. Dealer thinks they know better. What more is expert to do? Do you have to publish a book to be an expert?