If the Vin checks out good I would say,
"I could easily spend $1000 on this plus heaps of time on it, then press the start button and it still might not go, for $1000 you can get one that goes"
"Im looking for one in better condition that I'd pay more for, but the most I'd pay for this one is $200"
Then I'd promise myself to leave it as a parts bike and not spend any time trying to get it to run. I've made this promise to myself for two of the bricks I have, problem is I couldn't help myself and broke that promise both times.
If you don't get it, you've just saved yourself a heap of time.