Richard, your post caused me to remember circa 50 years back, while next in the queue at my local independent s/h m/cycle dealers workshop, the owner was a keen m/cyclist himself, the guy in front of me was in need of either a jet or a float for his Amal TT carb.... the shop owner pulled out a TT carb and stripped it down to to remove the required part, and once removed he told the chap the price, to which the reply was HOW MUCH... the dealer said nothing and just began to replace the part and rebuild the carb... At which point the chap seeking the part then said OK, OK, to which the owner replied that the part was now unavailable to the intended purchaser at any price...

At the time I was in the process of re- customising my recently acquired Norton Dommie into a cafe racer whereas the previous owner had tried to make into a chopper, kinda hints at the period of time... (-: I was also a semi regular at the dealership and had always found the owner to be a fair minded chap, thus I doubt that he was likely to have overpriced the required part...