Eric,
In a number of ways this was one of the very best grills Weber made (not including the car-priced Vieluxe).
I LOVE the stainless frame and the stainless cabinet pieces of the exclusive Platinum version of the Summit. These were great ideas that died with the short-lived Platinum name. The current version looks imposing but, lacking the stainless frame and cabinet parts, reduces to a pile of rust in our South Florida salt air:
This particular Platinum is the BEST of the bunch with its rear infrared burner and rotisserie setup.
Now, the very bad news: the firebox on these grills is part cast aluminum with the rest being porcelain plated regular steel. Possibly due to heat expansion and contraction and moisture held on by hot grease, the porcelain portion seems to crack, most particularly in the front where the burners go in. Then the rust monster goes to work leaving you an unsafe, unworkable grill. For this reason I have personally given up on Summits, except I admit this particular model still tempts.
Here is the firebox front on one of my current generation Summit projects, maybe a lost cause:
Why Weber didn’t use all cast aluminum like on the “lesser” Genesis is a mystery topic here on this forum.
The one you are looking at does appear lightly used and/or well cared for. I would CAREFULLY examine the inside front of the firebox. If there is rust and the seller is the original owner, see if you can get them to make a warranty claim. If there is rust but that is not an option consider carefully before buying. You might be able to purchase a replacement for the firebox front or perhaps get a sheet metal shop to fabricate a repair. Either, way your grill is going to cost a good bit more than just the initial purchase price.
It may well still be worth it to you if you have reason to need a large grill and want good space for rotisserie cooking.
There are a number of recent threads here about Summits that you can search for and I believe get some benefit.