I want as many details as they can give me about the property. I want to know what they owe, how long they've owned, what they've done to the place in terms of rehab, if they have any recent appraisals, what they want for the place, wether they'll do any seller financing and how, and most importantly in my eyes, why they're selling (not in any particular order).
I don't usually talk with them about what I could pay them for it right then. I focus on percentages of value that we're usually buying for in particular areas or the particular price we've paid for a property in the area. Going that route, I find out real quick whether they're interested in talking any more at that point without them feeling under attack or insulted. I know whether they're realistic and how much they're willing to talk.
I ask them to give me a little bit of time to pull comps and run the numbers and then if I think it makes sense, I'll get back to them. It's very non threatening and helps them to relax as we're talking as they realize I'm being straightforward. I then go pull comps and if we're close, I call or email and talk it through.
That first conversation is about getting as much information as possible and trying to take down some barriers. Then, when I call them back fairly quick, they see I'm responsible and someone of my word as well. Those are all factors that help them to let go, even if they really don't want to do it.
I know their are other ways of handling it, but that's worked well for me.