Keep in mind I'm new to pinball but here's my experience with White Water buying.
The problem I've had is that they're tough to find, even tougher to find in good shape, and when you do find one that appears to be in good shape then it's half way accross the Country and you can't really verifiy that it actually IS in good shape. So when you buy from somebody who's not local, you have to hope that they're honest and also pay another $500 in shipping (so a $3500 is now $4000) and hope it holds up in shipping.
The ramps on that one look original (they also look broken up near the lock targets), which means they're probably going to need replacing along with the rest of the ramps ($600). The boulders are cracked (replacing those is another $150 or so.) Add in plastics, targets, protectors to stop your new stuff from breaking, etc. etc. and you'll have another grand in it.
The playfield actually looks pretty good to me but you can see some spots. There's the possible planking under the flipper there but also look at the spot near the right slingshot. I have that exact same spot on mine. When you see that up close you're going to see the paint tearing up from wear. Expect to see more of that. That's not as important to me but for some people that means you need to have the playfield restored or replaced.
There was one in decent shape with a really nice playfield on Pinside a few weeks ago for $3500 and it was gone within an hour. Good deals like that don't seem to come up that often.
The thing is, I'm sure that one you linked to will sell for $3,500 to $4,000 so if you want it, you can't really lowball. It's a tough situation really. I sat and watched for years as the price rose. So it's really a matter picking your poison unless you get lucky or are well connected. If the playfield is nice and the cabinet is nice at least you know that you can replace all the ramps and plastics yourself. The cabinet itself looks really nice! If I were you I'd go play it and really really look it over thoroughly. If you can make a deal great. Just realize that you may have a $1000.00 in plastic replacement in your future and make sure you can live with that when you hand over the money. If you walk away, just make sure you can live with the fact that it may be a while before another one shows up locally that you can actually score.