Maybe I missed something here. Your watchmaker feels the watch had not been previously serviced. Is the movement broken or... not running due to old lubricant , soil, etc, etc. ?. If the movement needs a lube and tune ( a 100k mile service) I am not sure you have a legitimate gripe here. The dealer said it would need a service. You may have assumed the service would be a modest one, not a complete disassembly and cleaning.
In these type of situations I think we all hope for the best and plan for the worst.
I just scanned this thread again to see if I missed something. He refunded you half the service cost!. Quit while you are ahead. Oh, and name this dealer. Not to shame, but to allow members to be informed when dealing with him.