Although working with various instruments and having a large collection of books and catalogues and a vast knowledge of instruments, valuing instruments is the aspect of the business that Hein least likes to do, and will only undertake a valuation for insurance purposes for instruments that he feels confident about valuing.
A new instrument by a living maker can be replaced and can be valued by the maker with a replacement valuation.
Likewise a modern manufactured instrument can be replaced with one for the current price.
With old instruments, many factors play a role, such as the authenticity, which despite expertise and experience can be quite hard to confirm in a craft with a long tradition of copies and outright fakes!. The condition of the instrument also plays a role, an undamaged instrument is more valuable than a damaged one. A repaired instrument will always be worth less but the quality of the repairs also play an important role.
Never take a label in an instrument too literally. “Stradivarius” and other Italian names are usually more an indication of the rough model of the instrument, than anything else.