Very old instruments may need a lot of expensive repair. Bellows may have holes and need replacing - $$$$$$$$ - may need to be specially made if an unusual size. The leather valves may need replacing - 2 for each note on each side - reeds may need tuning or replacing if rusty, etc. The surface finish plastic on older instruments may be not the safer acetate, but the older nitrate - too much heat and it will explode into fire - as happened to Rolf Harris while his instrument was on stage in the heat from the lights... :-) He still played it after though!

The best 'old' instruments for tone, size, weight, playability, etc are those made in the 1950s-60s heyday. Older instruments MAY actually be wonderful - but, if not played or stored correctly, may have much expensive damage - mould, rust, damaged valves, the wax holding the reeds may have cracked, etc. Example, if the instrument has been stored on its back, the leather valves will have warped and need replacement or the sound will be terrible - they are meant to stand on their feet on the left hand side where the bass buttons are so that no strain is put on the valves. If stored subject to damp - mould. Ants may have eaten the felt/rubber (found one like that myself!), heat or cold may have damaged the wax, etc

An old instrument may be 'valuable' as a museum piece, or to hang on a pub wall and rust away, but as a playable item, it may need much work - I can't do it myself, so I have to pay, and good technicians are literally dieing on their feet nowadays - so it may not be a financial worthwhile project, but then again, you may be very lucky.

Old Italian instruments may actually be very good instruments, and some of them ARE really worth restoring for their tone, but it's a bit difficult to guess without looking closely at them.