Some concerns are the base under the spa looks pretty rotten, could have crept up into the actual base of the spa, the cover looks like it will need to be replaced soon. Crap shoot on if it will run or not or leak until you hook it up. Good news I don't know if Nashville got freezing weather or not, so you might be good on that.
I would say go look at it, open the front panel and see what is or isn't there and look under the cover as well. Offer 350 or 400 see if he takes it. 700 on a chance it will run and his word is a tough one! If enough people have looked at it and passed he may take the low offer.
Worse case you get it for 400 hook it up, fill it and it doesn't run could mean some dollars it it does run and holds water you got lucky.
You have to go with your gut on this one!