It seems likely that there's a sort of placebo effect at work, making people believe certain violins sound better or play better.
Elite Violinists Fail to Distinguish Legendary Violins From Modern Fiddles
If you know only one thing about violins, it is probably this: A 300-year-old Stradivarius supposedly possesses mysterious tonal qualities unmatched by modern instruments. However, even elite violinists cannot tell a Stradivarius from a top-quality modern violin, a new double-blind study suggests....
"There is nothing magical [about old Italian violins], there is nothing that is impossible to reproduce," says Olivier Charlier, a soloist who participated in the study and who plays a fiddle made by Carlo Bergonzi (1683 to 1747). However, Yi-Jia Susanne Hou, a soloist who participated in the study and who until recently played a violin by Bartolomeo Giuseppe Antonio Guarneri "del Gesù" (1698 to 1744), questions whether the test was fair. "Whereas I believe that [the researchers] assembled some of the finest contemporary instruments, I am quite certain that they didn't have some of the finest old instruments that exist," she says.