I have had great luck with Craig's list. All the stuff you guys just complained about is what I use to weed out the non serious buyers. First I always add a line to the end of my add to sort the stupid, it says "If you can see this add, the item is for sale. If you can't see this add it means it has sold." If I still get someone asking if it is still for sale I know to ignore them.
If someone tries to haggle on something they have not seen, I know they are not someone I want to deal with. If they ask stupid or irrelevant questions I ignore them. If they ask for ANYTHING out of the norm, I ignore them. If they ask for a payment method that is odd, I ignore them. I always have a back up story for the hagglers. I was selling a TV for $200.00, the guy asks me when he comes to look at the TV, will you take $100? I told him for anything less than $200 I would give it to the ex wife, and make her day. That stopped the negotiations and he handed me the $200. (I will donate it to my Church is another good negotiation killer)
I was selling a pellet stove, the first caller was a nice lady that asked about the stove. I told her I had people driving in from California and somewhere else this weekend to look at the stove. She said she figure they had priority, but if they didn't buy it she was very interested in coming to see it. I told her priority is the first buyer to show up with money, and it was not her fault that the other people couldn't come sooner. I told her she could come look at it that evening after work. She showed up with friends to help look it over, she bought it for the full $2200 without bothering to haggle, and was very happy to get it for that price compared to everything else she was looking at.
She also felt really good about her purchase because she thought she grabbed it before the other people got to look at it, I didn't see the harm in letting her feel good about her purchase. I even worked with her to help her order the parts she needed to do the exhaust piping.
So I have it pretty well mastered. The people will make it pretty clear if they are worth dealing with, just watch and listen for the clues. Ignore everyone that is even slightly out of the norm. You guys know what a normal purchase looks and feels like, if the person contacting you doesn't fall into that category, ignore them until Mr. normal contacts you. It takes patience, but not as much patience as dealing with the wackos that are not serious buyers.