I'm generally an avocado purist, so I throw out any brown spots, but I notice that many restaurants serve avocado even with the brown stuff...
When is an avocado considered bad, and when should the chef be notified that there's something wrong?
If it's fully green or even yellow the chances are it's still rock hard.
Personally a little brown on an avocado is a sign of ripeness,
I'd regard an avocado that's gone black as completely past it.