Worm War I is pretty rare. Not $600 rare, though. The 6 switch woody Telegames unit is also rare. Tends to be worth about twice as much as the standard version. The price is just stupid, of course. Maybe that person saw one on Pawn Stars or one of those auction shows that are so terrible.
Okay, I finally get to break out the book I got for Christmas: "Classic 80's Home Video Games ID & Value Guide". (These may be outdated, just a warning)
Worm War I goes for between $23 to $29 COMPLETE IN BOX depending on the version. Unboxed? $6 - $11
The "Heavy Sixer" Sears Telegrams system goes for $30 loose (maybe $80-$100 with all the controls, cords, etc.), the box would have brought it up to $185. Loose cartridges figure at $2 - $5 each for the more common titles (which was most of them but I really didn't check each one). Haunted House is a buck (again, loose).
So yeah, someone's overpaying or someone's seriously shilling.