I've had mixed results with CL and Ocala4sale.com.
Buying: I bought my tractor on Craigslist, and I got him down from $1500 down to $1400; but I had the money with me if he wouldn't budge. I got a 6 ft Frontier box blade for $190, list was $200; I told they guy (truefuly) that I had had $200 earlier in the week, but had spent the $10 since (lunch or gas or something). I really only try to spend about scrap value, that way your not taking much of a risk.
Selling: I've sold some ladders, a truck, and something else (forgot what) and every time it's been a pain in the butt. I try to meet people away from house because I don't like them eye balling everything. I've had no shows, people who offer 50%, ect.
Wife sells some stuff on Ebay with pretty good results. She normally lists at a bit lower than the minimum she wants, and always includes a Buy Out.
I've bought some stuff on ebay, in general not too disappointed; But... I've noticed a lot of re-re-sellers of imported stuff, who have no idea what they are selling. Bought a MK-180 crossbow, that was listed as a 180 lbs draw; after buying it ($72) and doing more research the manufacturer lists it as 130 lbs draw. ARC-180 welder, seller lists it as 180 amp; really is 135 amp. I've never sold on ebay myself, mostly because everything I would sell would cost more to ship than its worth.
I did have an eBayer get mad at me for asking a question. Add says 20# seed peanuts, $3.99... I message to ask, is that really 20 pounds? He say, I never said 20 pounds, you would have to be stupid to think I would sell 20 pounds for that. I had to inform him that the "#" typically would mean pounds/lbs, and if it's 20 individual seeds maybe try saying 20 each/pieces or something.