A Chevy Dealer isn't the first place I'd look to buy a Porsche.
They either took it in Trade, or they picked it up cheap at an auction in hopes of a quick turnaround, or as a 'sexy' stalking horse to attract buyers into the showroom. A 3rd possibility is that they have a leasing arm and this is a lease return, though the mileage looks a little high for that.
In either case, Boxsters are not their area of expertise. So, how did they prep/assess the car? Just a polish job and quick test drive?
That doesn't mean it may not be a good car. A quick run of the VIN in carfax shows 9 records (you have to pay to see what those records are). That doesn't seem to be a significant number of records, but the car has likely had multi-owners. Realize too that Carfax is not at all definitive, just another source and must not be taken as the sole source.
Price seems a little high in general. The cars for sale in this price range are typically in the 35k-45k mi. area, so they're not giving it away, though the ad isn't very specific on options (probably due to their unfamiliarity with the model), so no real way to assess the price.
But, at 60k mi., it's got a major service due and could be at the end of brakes and tires (probably 1st set of brakes and 2nd or 3rd set of tires for this mileage)
It's not the 1st car I would rundown because there are just too many of them on the market.
Have you check your area? There are a couple '04s in your price range:
And an '02:
http://www.automotive.com/2002/65/porsche/boxster/base/ohio/dayton/218140441/113/index.html?filter=postalCode%7c43068%7c&index=6
I saw 12 other Boxsters in the OH area as well. There really is no shortage of these. Realize too that you are buying just as the market for convertibles is starting upward, with Top Down weather not far away, so that will give you less negotiating room.
In any event, be sure to do a PPI (Pre-Purchase Inspection) by a qualified Porsche mechanic or independent. Ask to see service records.