We should compile a thread of knowledge for useful tips in you and others experience to avoid becoming the victim of online scams:
If the person contacting you uses the word "kindly", it's a scam.
If you list something on Craigslist and you are contacted by someone with an
@yahoo.com email address and they use unnatural sounding English, it's a scam.
If they are from Nigeria, it's a scam. Especially if they are a Prince in Nigeria asking your assistance in a money transferring scheme.
If they want to send you a cashier's check or money order or similiar, wait at least 10 business days after cashing it before furthering your agreement. Oftentimes they used forged documents that initially look legitimate but a few days later your bank withdraws the money and you're out of whatever you sold.
Be absolutely sure any emails you receive with links to your bank and/or credit card website actually go to that website. Firefox 2.0 and IE 7.0 both have built-in protection against most of these phishing websites. If ever in doubt, just call your financial institution and ask. Remember they already have your personal information and should never be requesting you to provide much more than your already chosen username/password.
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Easiest one for less savvy users to fall for. Always, always manually put in the url of the website you want to go to if it has anything to do with personal information and you have to log in.