Aside from the issue of abuse (caveat emptor applies there), the parts should last a long time. Drivers, per se, are unlikely to wear out, but surrounds eventually do. They are relatively inexpensive to replace, though. I've had surrounds last over 25 years, and amps at least that long.
So, if they are in "perfect condition" and haven't been abused, it can be a good gamble, although, as with anything used, something unexpected can occur and you have no warranty protection.
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