Depends on the specific deal. But generally speaking, if I was looking for a cab and saw an used one that's in good shape and the price is right, I wouldn't mind buying it used.
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Good quality cabs in general don't really suffer much, so I'd say it's safe to buy a used one if it's a good quality cab, say mesa's, orange's, the big marshall's, zilla's...

But yeah, as UG's Tony Stark said, if it's a good deal I wouldn't see why not going for it.
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if the cabinet is in good condtion id go used 90% of the time as the previous user will have used and worn in the speakers so your getting the best sound those speakers can produce without having to spend ages breaking them in yourself
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