I have used mostly Craigslist and Ebay (over 8-9 years, my ebay feedback is about 225 (about 5 or 6 for buying stuff -- all the rest for buying <y>). Mostly electronics/computer related.
On Craigslist, I usually limit the area I look in to be limited to about 10-12 miles. Live about 20 miles outside a large city -- but NEVER go into city tho. Prefer to meet sellers 'someplace', tho OK if I know their home area. Contacts sellers via email -- I won't respond to 'twitter' emails ads (or those who they say won't answer emails). Just be careful.
Stuff I have bought: 3-4 Apple iphone Touches (for me and a friend), IBM laptop (S10-c), Window OS (legally), Dell laptop, peripherals, small TVs, etc.
On ebay : too numerous to list. -- lot of (older) laptops, laptop parts, software,,,,,,
Good luck !