Typing jobs.

Do not send payment to a prospective "employer" for any reason (e.g. visa or processing fees). A legitimate employer will not ask you for fees and you will lose any money you send.
Beware of any "job offers" that require you to act as a "payment intermediary." You will be asked to receive payments via cashier's check, keep some percentage as a "payment fee", and then to wire a lesser amount to a third-party. The cashier's check will be fake and you will lose the amount sent to the third-party.
A distant seller or owner asks for payment via Western Union or MoneyGram. After payment is sent using one of these services, the distant owner promises to send item or keys via Fed Ex, DHL or other delivery service however the items or keys never arrive.
A common misconception is that the victim's bank account is requested so the culprit can plunder it -- this is not the primary reason for the account request -- merely a signal they have hooked another victim.