I turn down work too. For any number of reasons, but often it is when the potential client is not listening to me, and I can see that the expectations are not aligned with what can be done.

That said, these are often face to face meetings, or after an exchange of information that I know is meaningful. The good thing here is apparently work has not started. Perhaps they were being too honest with you, just not soon enough. I would think after a number of emails and images of the frame in its current state that this conclusion could have been arrived at prior to it being send over the border.

Color matching older paint I will say is tough, and the expectations are probably framed in reference to an autobody repair, where a known color of a late model car can be matched very close indeed, this is because the auto manufacturers push the various paint makers to match their standards with few exceptions. Bicycles are a not documented in comparison very well.

To play the devil's advocate, lets say they have to custom match the color, how much time to do this? one hour? two? Will they have to order a special toner from say House of Color to make it? With modern paint systems, getting to assess a comparable color might also include spraying the clear over it, while the color is not mentioned, Bianchi was doing this slightly pearl finish to their celeste (they might still be) that would be a terror to match or blend.

Communication is the key, face to face is best. Everything else falls short.

I will say after all that, the cyclart estimate process I reviewed way back would make me shy away from ever using them, way too much leeway. I think in many cases especially with their long term experience that they should be able to hold to a price, especially when no subletting is needed like chrome plating.