Nowadays scammers have been able to adapt extremely fast to the ever increasing defenses that many internet companies have installed. Web services like Google or yahoo have set massive defenses in place to filter out spam and scammer content yet every now and then these defenses are breached. here's some tips to avoid them,
1. A sense of urgency. With any format that a scam may come in their one similarity is the urgency they bring to the table. It may be written like so "The time is NOW to reclaim a loaded bank account ($200,000,00) that will expire if a small ($250) renewal fee is not payed" or " Your distant relatives excessively appraised estate is being auctioned off and the will states that you must IMMEDIATELY claim it with some paper work and a fee to get it processed very fast". This false urgency is used to land a target in a emotional state of panic and thus makes them more compliant to the scammers needs.
2. Quid pro quo tactics. If you come across a typical 419 scan a.k.a. the Advanced Fee Scam that gets written as follows. "X amount of money is here in this bank because Y. We need you to validate yourself with a small transfer fee and the money will be yours". The logic behind the scammer is that you will negate the risk with the prospect of a payout a few orders of magnitude larger than the "principle"
3. Bad grammar. Oddly enough the prolific use of broken English has become a staple in many scams. This is due to a heuristic technique that weeds out the smarter marks (a scams target) and leaves those that would be ignorant enough to continue the dialog.
4. Documentation. Often times documents will be added to verify a scammers validity when there's none in the first place. A simple cross reference will prove the scammer wrong in numerous ways. If the scammer was tempted enough to tie the document to a name of a bank or person of any public status you can always ask them directly regardless of what the predicament or "hook" a scammer throws at you to keep you talking to them only.
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