I love bingos - $700 for a Nashville I would expect to be in really good shape (the playfields normally do not wear on these badly due to coating), the backglass appears to be in good shape.
Nashville is a great 6 card bingo, and is the next to last 6 card EM bingo that Bally produced. As such, it has a ton of great features to help you play/win.
I have no familiarity with bingo pricing in the TN area. However, this machine would not be worth $700 for me. The cabinet looks like it has damage repaired with wood screws, and the coin door is scratched up. This brings the price down quite a bit to me.
I am not a gambling person, but I love the bingos. Easy to understand your goal, but requires a lot of skill and thinking to achieve. I find slots, even ones with advancing odds to be a poor comparison, since the bingos rely directly on the player's skill.
-Edit- One thing to keep in mind - the $700 is not that bad of a price when you factor in the amount person might have paid someone to shop it. There are some very skilled bingo technicians in that area, as well. Remember that the 200-400 prices you see may be for games that are not fully working (despite what the ad says). Be sure to test it with the glass off.
Nashville is a 10 coin max game. That means for each flick of the coin switch, a new feature will light. The first 6 are lighting the bingo cards, and the remainder light features. The magic number should be different each game. Test each game with all 10 features lit.