The allure of an older instrument, especially a cello, is completely understandable. Fine bowed stringed instruments often become better with age, and we are all hoping to run across the next 'Stradivari'! As the wood ages further, and the instrument has been played in by multiple players, the tonal quality usually improves; becoming more integrated, like a fine wine. However, just because an instrument is old doesn't necessarily mean it is going to be great. As a matter of fact, if you are thinking of purchasing an older instrument, say anything older than 100 years, here are a few things you should be aware of.
Older instruments can be more sensitive to weather changes, having 'bad hair days' whenever the pressure changes, or it becomes damp out. Since the wood has been very well aged (dry) after a hundred years or more, dampness is often the most problematic weather change for old cellos. The wood is very porous, and the resin in the wood has mostly dried, so these older instruments can act like sponges, soaking up extra moisture in the air. When this happens, the cello will suddenly sound 'dead'. There is nothing that can be done except to wait for it to dry out. If you live in an area where it is very damp, or with extreme humidity changes, we recommend that you keep the cello in a hard case when you are not playing it, and put a Boveda 2-Way humidity kit in with it. This will keep the inside of your case a constant humidity.
One issue we have seen with older instruments is the neck sagging. There is a lot of pressure constantly applied to the neck via the strings and bridge. If the maple neck grain was not well selected, over time, the scroll can go up, and the bridge end of the fingerboard go down, causing the strings to appear too high. Often, luthiers won't realize what has happened, and they will just lower the bridge. Then pretty soon you have a cello with no power. It is a rather expensive repair to correct a sagging neck, so if you are looking at an older instrument, have a luthier inspect the neck projection. If is is too low, either say "no", or be prepared to shell out $2,000 or more to have it fixed.
Old repairs inside an older cello can lead to a variety of annoying issues. Improperly repaired cracks can reopen, and the seams can tend to open more frequently due to the dryness of the wood. The bass bar can come loose and so can the purfling or old cleats. Consider an older cello like an old MG car; they both tend to need a lot of maintenance just to keep them going.
Often the setup on older instruments is outdated, and holding back what might otherwise be a great sounding instrument. Newer, lighter and better designed parts are now available that weren't 100+ years ago. The tailpieces are lighter, as are the endpins and fittings. Upgrading fittings like these will usually make a good instrument sound amazing. But that setup work comes with a cost. Expect to pay $800 or more for a really good setup on a used instrument. This would include strings, tailpiece, correcting peg issues, new endpin and fitting, etc.
Labels... this is a deep subject for which we are not experts, but be aware that just because your label says one thing doesn't necessarily mean it is that thing. Even 200 years ago makers were faking labels, so some older instruments with really old labels may not be what they say they are. If you are looking at spending 5+ figures on an older instrument and you think it is X, it's advised that you should have it examined by an expert in cello makers, especially if you are purchasing it as an investment. Even then, identifying older makers is an art, not a science, and is all based on the education, experience and opinion of a person long removed from the actual making of the instrument.
If, in the end, you decide an older instrument is for you, consider yourself its temporary guardian; these things live a long time and you will undoubtedly not be its last human. Take as good care of it as you possibly can. Some day, it will move on...