I know there is craigslist, amazon, and eBay. But do not know what site to place it on. I would post it on all three but the only problem is that if I get two orders for the same item, then I will be in a bad situation. Or is there a way to post it on all three of them but if lets say someone buys it off of eBay, then it will be taken off of craigslist and amazon? If not, what's site has a better chance of items being sold or making the most money?
I agree with Rebecca. Ebay is nice because there are potential buyers worldwide, but there is also lots of competition on selling prices of the same item. Also, you'll be charged a fee for the sale and you'll have to ship the item. Craigslist is nice because you can find a local buyer…no extra fees and hopefully no shipping. But it might time a little more time to sell the item. Good luck!
Craigslist is by far the easiest.

Just remember cash only and never ship anywhere.

Ian Drake
http://www.NotifyWire.com - Craigslist search and monitoring
Craigslist is best since they don't charge fees like Ebay does. Ebay and paypal can really screw you on charges.