I know static electricity can mess them up. So they can pretty much only break if you dont handle properly or drop them. It's only 11 bucks so it might be worth a shot.
Some shops put grounding straps around there wrists when working on them. I'm not 100% sure if this is only for 96 cars with all the On Board Computer stuff or if static electricity is something to worry about with our older cars also.
I doubt it's bad... The odds of a bad computer are pretty rare.. It can happen though, if the user's got decent feedback I doubt there will be a problem..
Yes, they can definitely go bad. I had mine go out a year or two ago, not really sure why though -- no jumpstarting or anything. Like mentioned above, I would just go off the feedback of the seller.