Pros: Amazon is convenient, fast and simple. The site allows you to attach your item directly to the Amazon listing for the product, so anyone shopping for a specific product will see your item listed along with the new ones. You can even ship your items using the Fulfillment by Amazon Program, and Amazon will take care of everything for you. Amazon is great for selling cheaper and more common items.
Cons: The fees for listing on Amazon are high, and Amazon takes a pretty big cut of the selling price. It can also take Amazon up to 14 days to pay sellers for their sold items. High-priced items and obscure items are difficult to sell on Amazon, or the seller doesn't receive a high return.
Pros: Craigslist, essentially a classifieds site, allows you to set your own price and no third party takes a cut. The site allows you to sell to your community directly instead of the Internet at large, and that may work to your advantage since more people in your community may be surfing Craigslist for bargains.
Cons: Selling directly to your community rather than the Internet at large shrinks your audience, and you might waste months waiting for a decent offer. Craiglist also tends to draw in a wide array of users, and it's not uncommon for sellers to get scammed. Someone might show up to make a sale, but try to weasel out of the deal or sway you to take less for your item than they originally promised you. There are also infamous safety concerns with Craigslist; Lifehacker created a guide on how to safely sell on Craigslist.
Pros: Your items will be certain to sell on eBay if you price your stuff closer to or better than the competition. eBay has a global reach and lists everything and anything you might want to sell, and is great for selling high-valued and obscure items.
Cons: You need to carefully craft your listing to make sure it's easily found, eye-catching and better than the competition, because it's difficult to sell common items on eBay. The site also takes a pretty high cut of the sold price, and eBay has removed seller protections almost completely and sides with the buyer in almost every dispute. It's not uncommon for buyers to scam or take advantage of sellers by telling eBay that they want a refund, and the seller is out both the item they sold and the money they should've gotten.
Pros: Facebook, the world's largest social network, is also a storehouse of sale groups. All you have to do is search for your state or region along with the word "sell" or "buy" to find local groups to buy, sell and trade your stuff. If you can't find a group in your area, you can always start your own. With Facebook groups, you have the option to decide whether you're willing to ship an item or whether you'd rather the buyer come pick it up. You can set your own price, and no third party takes a cut of your sale price. You can also see exactly who you're selling to and can avoid potential scams.
Cons: Many groups are closed, so you have to ask permission to join. Some groups only accept certain types of listings, so you have to read up on the group's rules before you try to make a sale. Additionally, to weed out the scammers, some groups have strict requirements on how many items you can try to sell per day.