I'd jump at it for $400 if there was no wear on the playfield. Good deals are usually gone in minutes, so you might be too late already.

I'm not sure what you mean by "authentic". Counterfeit pinball machines don't really exist, unlike with smaller collectibles and antiques.

The "factory settings" means that the saved settings were lost and the factory default settings were used. Usually this means there might be a battery problem, battery damage, missing batteries, faulty RAM, etc.

If the key is lost, usually it's easiest just to drill out the lock and install a new one. Locks are cheap.

I usually wrap games in 80 gauge stretch wrap and pack with blankets. When the backbox folds down, I use a piece of of a swim noodle slit lengthwise (or a piece of pipe insulation) on the top edge of the backbox. Or, a couple of layers of cardboard work ok too. Padding is necessary, or you will cause damage.

With the right tools, you can move a pinball machine by yourself.

If you have never owned or worked on a pinball machine you have a bit of reading and learning to do.

The batteries and circuit boards are in the backbox. You will need to unlock the backbox, lift up the backglass panel, carefully swing it out towards you, then lower it down.

It's not a good idea just to pop some batteries in, especially if the old ones leaked. Plus, the new ones may leak. There are a few different ways to handle the battery problem. Here are a bunch of helpful links that should get you started:

http://www.ipdb.org/machine.cgi?id=617
http://www.pinwiki.com/wiki/index.php?title=Post-Purchase_Checklist
http://www.pinwiki.com/wiki/index.php?title=General
http://www.pinwiki.com/
http://pinwiki.com/wiki/index.php?title=Williams_System_9_-_11
https://pinside.com/pinball/forum/topic/cleaning-and-waxing-pinball-machines-vids-guide
https://pinside.com/pinball/forum/topic/about-bullet-proofing-system-11-power-supply-vids-guide
https://pinside.com/pinball/forum/topic/vids-guide-to-upgradingrebuilding-flippers
https://pinside.com/pinball/forum/topic/vids-guide-to-rebuilding-pop-bumpers

But, yes, as the others have said, it's a good deal, so get it now, and worry about some of the minor repair details later. You'll have plenty of time to read & research later.

Isn't it 5/8"? I can't remember--I don't have my toolbox sitting next to me.

You can use an adjustable wrench in a pinch if you don't have a socket set handy. It's not quite as fast, but it will get the job done.

[edit]: It could be either 3/8" or 5/8", depending on the game or if someone replaced them at some point.

I can see wear spots where the balls drop into the inlanes from the ramps. I can't definitively tell if there is wear anywhere else.