I think the dealer was trying to take advantage of someone who wasn't sure of its value.
1903 prices can get pretty high, in good shape, among the Curio & Relic list group. I don't think I've ever seen one that wasn't absolute junk (or a parts gun) that sold for anything like $150.
Try subscribing to that list, and see what they have to say. You might even get some offers, if you put a good description and price in your message.
Here's the address. Put the subject in an otherwise empty message.
______ C&R FFL LIST
E-mail: subscribe c-r-ffl
to firstname.lastname@example.org to be ADDED
E-mail: unsubscribe c-r-ffl
to email@example.com to be REMOVED