Generally speaking, if something is for sale and I find the price reasonable, I generally don't have an issue buying it. There have been a few times that the purchase was soured a bit by the seller basically being in a bad way, but I figure the best thing I can do for him/her is buy the thing, as they need the money more than my pity.
This is what happened when I got my PS3. I got it from a guy on Craigslist for $120 (when they were going in store for $400), came with one game and no controllers. Went to the guys apartment, had just missed him as he thought he had time to go shopping with his family. Told him it wasn't a problem and waited for him. He rolled up an hour later with his very pregnant wife and six kids, then loaded all their food into the small studio apartment they lived in. That was two or so years ago and the system still works fine, so the only reason I could see for him selling it so low was the lack of controller and the extreme need for funds.
That...strikes me as a bad reason to become a collector. This has "future hoarder" written all over it.