buying used

The first thing I do is search for another one just like on eBay, craigslist, Gbase, etc.
If I find one and it's priced the same then I move onto things that are important to me pickups, frets, feel, tone, feel, etc
I'd ask if the bass has ever been serviced.
If all the parts are original.
If I'm comfortable turning a truss rod, and the seller is cool, I'd turn it 1/4 turn in both directions to be sure it's not frozen or the threads aren't gummed up. If you've never turned a truss rod I wouldn't suggest trying it on somebody else's bass.
If all those things check out then I'd maybe ask if they would sell it for $700 cash right now. I make I sure I have the cash in case they say yes. Well, that's if they're asking $750. I don't like to low ball as it seems to turn people away and IMO it's kind of a lame thing to do. I like to offer something that is fair to both parties.
Just my 0.02 cents

 

With a bass that new you're probably not going to find much wrong structurally unless the bass has been abused. Check that the volume and tone pots turn smootly and that there aren't any obvious flaws with the bass.

 

That price is good if the bass comes with a hard case.
It's still under warranty, so I wouldn't mess with the truss rod.
Just make sure you like the way it plays and sounds.

 

Best thing about buying used:

If you buy at the right price and you don't like it you can easily get your money back, or keep any loss to a small minimum.

Research some just like it and what they sold for, then make your decision smartly.

 

As long as he has (or can get) the original sales receipt.

 

Check for dead spots.... notes that choke and die or unpleasant overtones. Any of those conditions is a deal breaker regardless of price. IMO