I've only purchased from an operator once, and the circumstances were unique:

1) Another collector informed me of the game, and had spoken to the operator before about buying it, so there was a level of baseline interest.
2) The game was turned off at the location and thus not making money (game ran but was not fully functional, e.g., slingshots not working).
3) I called the *location* and got a hold of the operator while he was there (shear luck, I was just calling to confirm the game was still on location).
4) On the phone I asked if the op was willing to sell still and immediately agreed upon a price.

Note, even with all this, it wasn't smooth. I was not a priority issue to the op. He cancelled the first meeting with me and I had to play it day-to-day as he was noncommittal on even rescheduling. We'd agree on a follow-up time just to try and schedule a pick-up. I finalized it by calling on a day (at the location again, rather than the op direct), said I had the cash and could be there in a couple hours. He agreed, I went and got the game (with help; he made clear he wasn't going to assist in moving it at all but I'd never have assumed otherwise).

So, it took a bit of work on my end, for a game that wasn't making him any money (and the business was fine with him just leaving there in a corner). I did get a good deal for what condition it was in. The funny thing was, once I was there, he was interested in trying to sell more (an arcade game in this instance). In this op's case, I think he couldn't be bothered to really try to sell games since there was no pressure to get them out of the location, but likewise since they were making him nothing the idea of cash in hand outweighed the desire to keep them around... so long as there was next to no work on his part.

Anyway, don't know if that helps, but it's the only first-hand example I have of dealing with an op. As per JP itself, I got one last year within the Pinside average range. I watched a number of them pop up for more than I wanted to spend. I think I watched local listings for 18 months or so. For games like JP (with large production counts) you should likely be able to stay close to Pinside ranges if you don't mind waiting and watching. As others have noted, helps to know other collectors as they can keep an eye out for deals for you.