I agree, $8K before tax is kind of high (top case notwithstanding). People on this board have paid that or not much more before TTL for the bikes brand new.
On the other hand, based on other messages on this board, it seems 2012 DL650s have been harder to find in the Pacific NW area than, say, in the Southeast or Midwest. So you may have to factor in How Bad Do You Want It And When Would You Get It Otherwise, and how easy it is to get a hold of this one.
Just to play Devil's Advocate, if you end up paying under MSRP of $7,995 plus tax (6.5% in Washington State) = just over $8,500 for a new 2012 DL650, that sounds much better than the same $8500 for a used one with a top case and 1600 miles on it... Unless you aren't able to find that new bike for that price (a) without traveling over 100 miles to get it, (b) paying $600 or so in shipping costs to get a bike sent to you from out of state, or (c) even if you get a bike from a local dealer, having to wait until September or something. When you think of it that way, suddenly essentially paying someone a "finder's fee" consisting of letting them break the bike in for you (and paying for or taking care of the first servicing) while buying you a top case and riding it to your door may not seem so bad.
If you're the only buyer and he's the only seller, try to meet somewhere in the middle. Like offering him $8K but with your tax cost factored in, i.e., $7500, without the top case.