How much to phone qualify?

[Minna Reid]

When talking to people before you see their house, how far do you go to qualify them? I generally get their property description, their situation and what they think their house is worth, what they want for it, and what they owe. But I come accross a few problems. I'd like to save some time in not visiting people if their numbers are ridiculous, but at the same time once we're face to face they're generally much more forthcoming about things.
For example I talked to a couple and I really didnt even want to go as I figured I'd just end up telling them they should just find a realtor, and as it turns out, they really needed out and just jumped on my offer.
Then yesterday I saw another that I was excited about as the hubby sounded pretty realistic, but once I get there I realize we're like 80 grand away from any real price and needless to say he didnt care for my offer.
Couldn't I be qualifying better somehow on the phone so as my time is directed the right way? or should I always just go and see whats up?