One thing is, some people who are willing to give stuff away or sell it for cheap aren't willing to go into a lot of trouble to do so. I'm among those who don't like selling or giving away things to people I don't know! When I do, I usually put a price on the ads so things will go very fast! Last year, I sold a pickup truck in less than 24 hours after I placed the ad and this year, I did the same with a snowblower! I removed the ads quickly to stop getting emails and phone calls!
When I buy stuff for cheap or get stuff that's free, I make sure I can get the item in my truck or in a car that can haul what I'm getting. Unless the condition of the item is terrible, I just take it and I don't bother making any tests. I just grab it and figure that I will see later... I know it's not possible for everyone to do so but that's what I do. If the thing I'm looking for happens to be in really bad condition. I just part it out or scrap it.
On some occasions, I ended offering some money to people who wanted to give stuff. Earlier this year, I called to get a GE P400 percolator that was advertised at $8. When was on my way to pick it up, I got a phone call from the owner as her husband noticed it was missing the filter basket... I told her I'd get it anyway, that I already had one. So she said fine and she also said it was going to be free. When I saw it was in great condition, I didn't hesitate to pay the asking price, she refused the money but I insisted!
Last year, I got a KDS-58 dishwasher which had been built-in (so it was missing a few parts) that was advertised for free and I ended giving $20 to it's owner who was very kind and helpful.
And I recently offered $80 for an Inglis washer/dryer set that I wanted badly (and that was also advertised for free!) but that was already promised to someone who was going to pick it up for the scrap who had called just before I did. I could have taken a chance and offered less but I decided not to! I ended getting the machines and paying the owner $80 and he seemed very happy about that! If these machines would have been advertised at $100, I would have probably grabbed them anyway!
I tend to be more greedy when I deal with large corporations or with some professionals who exaggerate on the amount they charge for their services... Also, when people advertise something for far more than what it's worth, I sometimes call anyway. If we can agree on a price and I can inspect further to see the condition, it's fine.
One time, there was a 1960 French-Door range in bad shape advertised at $300, I went to see it as it was just a few blocks away from a friend's home. When I saw it, it was worse than on the pictures in the ad and I didn't want it. I still bothered to offer $30 to it's owners who where mad when I did so! My friend who came to see it with me was ashamed of my offer and embarrassed with their reaction! He then told me I should just have told the sellers I wasn't interested, but that time, I didn't feel like doing that! I knew they would end throwing it away and probably regret not to have someone to get it out of their basement and paying them to do it!